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tocCollapsibleButton_TO0P">On this page</button></div><div class="theme-doc-markdown markdown"><h1>实现 apply/call/bind</h1><h2 class="anchor anchorWithHideOnScrollNavbar_WYt5" id="apply">apply<a href="#apply" class="hash-link" aria-label="Direct link to apply" title="Direct link to apply"></a></h2><h3 class="anchor anchorWithHideOnScrollNavbar_WYt5" id="1-语法">1. 语法<a href="#1-语法" class="hash-link" aria-label="Direct link to 1. 语法" title="Direct link to 1. 语法"></a></h3><div class="language-jsx codeBlockContainer_Ckt0 theme-code-block" style="--prism-color:#393A34;--prism-background-color:#f6f8fa"><div class="codeBlockContent_biex"><pre tabindex="0" class="prism-code language-jsx codeBlock_bY9V thin-scrollbar"><code class="codeBlockLines_e6Vv"><span class="token-line" style="color:#393A34"><span class="token plain">func</span><span class="token punctuation" style="color:#393A34">.</span><span class="token method function property-access" style="color:#d73a49">apply</span><span class="token punctuation" style="color:#393A34">(</span><span class="token plain">thisArg</span><span class="token punctuation" style="color:#393A34">,</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">[</span><span class="token plain">argsArray</span><span class="token punctuation" style="color:#393A34">]</span><span class="token punctuation" style="color:#393A34">)</span><span class="token punctuation" style="color:#393A34">;</span><br></span></code></pre><div class="buttonGroup__atx"><button type="button" aria-label="Copy code to clipboard" title="Copy" class="clean-btn"><span class="copyButtonIcons_eSgA" aria-hidden="true"><svg class="copyButtonIcon_y97N" viewBox="0 0 24 24"><path d="M19,21H8V7H19M19,5H8A2,2 0 0,0 6,7V21A2,2 0 0,0 8,23H19A2,2 0 0,0 21,21V7A2,2 0 0,0 19,5M16,1H4A2,2 0 0,0 2,3V17H4V3H16V1Z"></path></svg><svg class="copyButtonSuccessIcon_LjdS" viewBox="0 0 24 24"><path d="M21,7L9,19L3.5,13.5L4.91,12.09L9,16.17L19.59,5.59L21,7Z"></path></svg></span></button></div></div></div><p><strong>参数</strong></p><p><code>thisArg</code></p><p>在 func 函数运行时使用的 this 值。</p><p><code>argsArray</code></p><p>一个数组或者类数组对象，其中的数组元素将作为单独的参数传给 func 函数。如果该参数的值为 null 或 undefined，则表示不需要传入任何参数。</p><p><strong>返回值</strong></p><p>使用指定的 this 值和参数调用函数的结果。</p><h3 class="anchor anchorWithHideOnScrollNavbar_WYt5" id="2-流程图">2. 流程图<a href="#2-流程图" class="hash-link" aria-label="Direct link to 2. 流程图" title="Direct link to 2. 流程图"></a></h3><p><img loading="lazy" src="https://user-images.githubusercontent.com/17525377/147632530-34eac628-0bbd-4025-890b-2596a421263d.jpg" alt="apply" class="img_ev3q"></p><h3 class="anchor anchorWithHideOnScrollNavbar_WYt5" id="3-编写代码">3. 编写代码<a href="#3-编写代码" class="hash-link" aria-label="Direct link to 3. 编写代码" title="Direct link to 3. 编写代码"></a></h3><div class="language-jsx codeBlockContainer_Ckt0 theme-code-block" style="--prism-color:#393A34;--prism-background-color:#f6f8fa"><div class="codeBlockContent_biex"><pre tabindex="0" class="prism-code language-jsx codeBlock_bY9V thin-scrollbar"><code class="codeBlockLines_e6Vv"><span class="token-line" style="color:#393A34"><span class="token class-name">Function</span><span class="token punctuation" style="color:#393A34">.</span><span class="token property-access">prototype</span><span class="token punctuation" style="color:#393A34">.</span><span class="token method-variable function-variable method function property-access" style="color:#d73a49">apply</span><span class="token plain"> </span><span class="token operator" style="color:#393A34">=</span><span class="token plain"> </span><span class="token keyword" style="color:#00009f">function</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">(</span><span class="token parameter">thisArg</span><span class="token parameter punctuation" style="color:#393A34">,</span><span class="token parameter"> argsArray</span><span class="token punctuation" style="color:#393A34">)</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">{</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token keyword control-flow" style="color:#00009f">if</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">(</span><span class="token keyword" style="color:#00009f">typeof</span><span class="token plain"> </span><span class="token keyword" style="color:#00009f">this</span><span class="token plain"> </span><span class="token operator" style="color:#393A34">!==</span><span class="token plain"> </span><span class="token string" style="color:#e3116c">"function"</span><span class="token punctuation" style="color:#393A34">)</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">{</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token keyword control-flow" style="color:#00009f">throw</span><span class="token plain"> </span><span class="token keyword" style="color:#00009f">new</span><span class="token plain"> </span><span class="token class-name">TypeError</span><span class="token punctuation" style="color:#393A34">(</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token string" style="color:#e3116c">"Function.prototype.apply was called on which is not a function"</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">)</span><span class="token punctuation" style="color:#393A34">;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">}</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain" style="display:inline-block"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token keyword control-flow" style="color:#00009f">if</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">(</span><span class="token plain">thisArg </span><span class="token operator" style="color:#393A34">===</span><span class="token plain"> </span><span class="token keyword nil" style="color:#00009f">undefined</span><span class="token plain"> </span><span class="token operator" style="color:#393A34">||</span><span class="token plain"> thisArg </span><span class="token operator" style="color:#393A34">===</span><span class="token plain"> </span><span class="token keyword null nil" style="color:#00009f">null</span><span class="token punctuation" style="color:#393A34">)</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">{</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> thisArg </span><span class="token operator" style="color:#393A34">=</span><span class="token plain"> </span><span class="token dom variable" style="color:#36acaa">window</span><span class="token punctuation" style="color:#393A34">;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">}</span><span class="token plain"> </span><span class="token keyword control-flow" style="color:#00009f">else</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">{</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> thisArg </span><span class="token operator" style="color:#393A34">=</span><span class="token plain"> </span><span class="token known-class-name class-name">Object</span><span class="token punctuation" style="color:#393A34">(</span><span class="token plain">thisArg</span><span class="token punctuation" style="color:#393A34">)</span><span class="token punctuation" style="color:#393A34">;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">}</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain" style="display:inline-block"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token comment" style="color:#999988;font-style:italic">// 将 func 放入 thisArg 内，这样在调用 thisArg[func] 时 this 自然就指向了 thisArg</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token keyword" style="color:#00009f">const</span><span class="token plain"> func </span><span class="token operator" style="color:#393A34">=</span><span class="token plain"> </span><span class="token known-class-name class-name">Symbol</span><span class="token punctuation" style="color:#393A34">(</span><span class="token string" style="color:#e3116c">"func"</span><span class="token punctuation" style="color:#393A34">)</span><span class="token punctuation" style="color:#393A34">;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> thisArg</span><span class="token punctuation" style="color:#393A34">[</span><span class="token plain">func</span><span class="token punctuation" style="color:#393A34">]</span><span class="token plain"> </span><span class="token operator" style="color:#393A34">=</span><span class="token plain"> </span><span class="token keyword" style="color:#00009f">this</span><span class="token punctuation" style="color:#393A34">;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain" style="display:inline-block"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token keyword" style="color:#00009f">let</span><span class="token plain"> result</span><span class="token punctuation" style="color:#393A34">;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain" style="display:inline-block"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token keyword control-flow" style="color:#00009f">if</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">(</span><span class="token plain">argsArray </span><span class="token operator" style="color:#393A34">&&</span><span class="token plain"> </span><span class="token keyword" style="color:#00009f">typeof</span><span class="token plain"> argsArray </span><span class="token operator" style="color:#393A34">===</span><span class="token plain"> </span><span class="token string" style="color:#e3116c">"object"</span><span class="token plain"> </span><span class="token operator" style="color:#393A34">&&</span><span class="token plain"> </span><span class="token string" style="color:#e3116c">"length"</span><span class="token plain"> </span><span class="token keyword" style="color:#00009f">in</span><span class="token plain"> argsArray</span><span class="token punctuation" style="color:#393A34">)</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">{</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token comment" style="color:#999988;font-style:italic">// 此处使用 Array.from 包裹让其支持形如 { length: 1, 0: 1 } 这样的类数组对象，直接对 argsArray 展开将会执行出错</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> result </span><span class="token operator" style="color:#393A34">=</span><span class="token plain"> thisArg</span><span class="token punctuation" style="color:#393A34">[</span><span class="token plain">func</span><span class="token punctuation" style="color:#393A34">]</span><span class="token punctuation" style="color:#393A34">(</span><span class="token spread operator" style="color:#393A34">...</span><span class="token known-class-name class-name">Array</span><span class="token punctuation" style="color:#393A34">.</span><span class="token keyword module" style="color:#00009f">from</span><span class="token punctuation" style="color:#393A34">(</span><span class="token plain">argsArray</span><span class="token punctuation" style="color:#393A34">)</span><span class="token punctuation" style="color:#393A34">)</span><span class="token punctuation" style="color:#393A34">;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">}</span><span class="token plain"> </span><span class="token keyword control-flow" style="color:#00009f">else</span><span class="token plain"> </span><span class="token keyword control-flow" style="color:#00009f">if</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">(</span><span class="token plain">argsArray </span><span class="token operator" style="color:#393A34">===</span><span class="token plain"> </span><span class="token keyword nil" style="color:#00009f">undefined</span><span class="token plain"> </span><span class="token operator" style="color:#393A34">||</span><span class="token plain"> argsArray </span><span class="token operator" style="color:#393A34">===</span><span class="token plain"> </span><span class="token keyword null nil" style="color:#00009f">null</span><span class="token punctuation" style="color:#393A34">)</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">{</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> result </span><span class="token operator" style="color:#393A34">=</span><span class="token plain"> thisArg</span><span class="token punctuation" style="color:#393A34">[</span><span class="token plain">func</span><span class="token punctuation" style="color:#393A34">]</span><span class="token punctuation" style="color:#393A34">(</span><span class="token punctuation" style="color:#393A34">)</span><span class="token punctuation" style="color:#393A34">;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">}</span><span class="token plain"> </span><span class="token keyword control-flow" style="color:#00009f">else</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">{</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token keyword control-flow" style="color:#00009f">throw</span><span class="token plain"> </span><span class="token keyword" style="color:#00009f">new</span><span class="token plain"> </span><span class="token class-name">TypeError</span><span class="token punctuation" style="color:#393A34">(</span><span class="token string" style="color:#e3116c">"CreateListFromArrayLike called on non-object"</span><span class="token punctuation" style="color:#393A34">)</span><span class="token punctuation" style="color:#393A34">;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">}</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain" style="display:inline-block"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token keyword" style="color:#00009f">delete</span><span class="token plain"> thisArg</span><span class="token punctuation" style="color:#393A34">[</span><span class="token plain">func</span><span class="token punctuation" style="color:#393A34">]</span><span class="token punctuation" style="color:#393A34">;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain" style="display:inline-block"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token keyword control-flow" style="color:#00009f">return</span><span class="token plain"> result</span><span class="token punctuation" style="color:#393A34">;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"></span><span class="token punctuation" style="color:#393A34">}</span><span class="token punctuation" style="color:#393A34">;</span><br></span></code></pre><div class="buttonGroup__atx"><button type="button" aria-label="Copy code to clipboard" title="Copy" class="clean-btn"><span class="copyButtonIcons_eSgA" aria-hidden="true"><svg class="copyButtonIcon_y97N" viewBox="0 0 24 24"><path d="M19,21H8V7H19M19,5H8A2,2 0 0,0 6,7V21A2,2 0 0,0 8,23H19A2,2 0 0,0 21,21V7A2,2 0 0,0 19,5M16,1H4A2,2 0 0,0 2,3V17H4V3H16V1Z"></path></svg><svg class="copyButtonSuccessIcon_LjdS" viewBox="0 0 24 24"><path d="M21,7L9,19L3.5,13.5L4.91,12.09L9,16.17L19.59,5.59L21,7Z"></path></svg></span></button></div></div></div><h2 class="anchor anchorWithHideOnScrollNavbar_WYt5" id="call">call<a href="#call" class="hash-link" aria-label="Direct link to call" title="Direct link to call"></a></h2><h3 class="anchor anchorWithHideOnScrollNavbar_WYt5" id="1-语法-1">1. 语法<a href="#1-语法-1" class="hash-link" aria-label="Direct link to 1. 语法" title="Direct link to 1. 语法"></a></h3><div class="language-jsx codeBlockContainer_Ckt0 theme-code-block" style="--prism-color:#393A34;--prism-background-color:#f6f8fa"><div class="codeBlockContent_biex"><pre tabindex="0" class="prism-code language-jsx codeBlock_bY9V thin-scrollbar"><code class="codeBlockLines_e6Vv"><span class="token-line" style="color:#393A34"><span class="token plain">func</span><span class="token punctuation" style="color:#393A34">.</span><span class="token method function property-access" style="color:#d73a49">call</span><span class="token punctuation" style="color:#393A34">(</span><span class="token plain">thisArg</span><span class="token punctuation" style="color:#393A34">,</span><span class="token plain"> arg1</span><span class="token punctuation" style="color:#393A34">,</span><span class="token plain"> arg2</span><span class="token punctuation" style="color:#393A34">,</span><span class="token plain"> </span><span class="token spread operator" style="color:#393A34">...</span><span class="token punctuation" style="color:#393A34">)</span><br></span></code></pre><div class="buttonGroup__atx"><button type="button" aria-label="Copy code to clipboard" title="Copy" class="clean-btn"><span class="copyButtonIcons_eSgA" aria-hidden="true"><svg class="copyButtonIcon_y97N" viewBox="0 0 24 24"><path d="M19,21H8V7H19M19,5H8A2,2 0 0,0 6,7V21A2,2 0 0,0 8,23H19A2,2 0 0,0 21,21V7A2,2 0 0,0 19,5M16,1H4A2,2 0 0,0 2,3V17H4V3H16V1Z"></path></svg><svg class="copyButtonSuccessIcon_LjdS" viewBox="0 0 24 24"><path d="M21,7L9,19L3.5,13.5L4.91,12.09L9,16.17L19.59,5.59L21,7Z"></path></svg></span></button></div></div></div><p><strong>参数</strong></p><p><code>thisArg</code></p><p>在 func 函数运行时使用的 this 值。</p><p><code>arg1, arg2, ...</code></p><p>指定的参数列表。</p><p><strong>返回值</strong></p><p>使用指定的 this 值和参数调用函数的结果。</p><h3 class="anchor anchorWithHideOnScrollNavbar_WYt5" id="2-流程图-1">2. 流程图<a href="#2-流程图-1" class="hash-link" aria-label="Direct link to 2. 流程图" title="Direct link to 2. 流程图"></a></h3><p><img loading="lazy" src="https://user-images.githubusercontent.com/17525377/147632668-575c348e-96f5-4088-8cee-38e3ee70a2cc.jpg" alt="call" class="img_ev3q"></p><h3 class="anchor anchorWithHideOnScrollNavbar_WYt5" id="3-编写代码-1">3. 编写代码<a href="#3-编写代码-1" class="hash-link" aria-label="Direct link to 3. 编写代码" title="Direct link to 3. 编写代码"></a></h3><div class="language-jsx codeBlockContainer_Ckt0 theme-code-block" style="--prism-color:#393A34;--prism-background-color:#f6f8fa"><div class="codeBlockContent_biex"><pre tabindex="0" class="prism-code language-jsx codeBlock_bY9V thin-scrollbar"><code class="codeBlockLines_e6Vv"><span class="token-line" style="color:#393A34"><span class="token class-name">Function</span><span class="token punctuation" style="color:#393A34">.</span><span class="token property-access">prototype</span><span class="token punctuation" style="color:#393A34">.</span><span class="token method-variable function-variable method function property-access" style="color:#d73a49">call</span><span class="token plain"> </span><span class="token operator" style="color:#393A34">=</span><span class="token plain"> </span><span class="token keyword" style="color:#00009f">function</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">(</span><span class="token parameter">thisArg</span><span class="token parameter punctuation" style="color:#393A34">,</span><span class="token parameter"> </span><span class="token parameter spread operator" style="color:#393A34">...</span><span class="token parameter">argsArray</span><span class="token punctuation" style="color:#393A34">)</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">{</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token keyword control-flow" style="color:#00009f">if</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">(</span><span class="token keyword" style="color:#00009f">typeof</span><span class="token plain"> </span><span class="token keyword" style="color:#00009f">this</span><span class="token plain"> </span><span class="token operator" style="color:#393A34">!==</span><span class="token plain"> </span><span class="token string" style="color:#e3116c">"function"</span><span class="token punctuation" style="color:#393A34">)</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">{</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token keyword control-flow" style="color:#00009f">throw</span><span class="token plain"> </span><span class="token keyword" style="color:#00009f">new</span><span class="token plain"> </span><span class="token class-name">TypeError</span><span class="token punctuation" style="color:#393A34">(</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token string" style="color:#e3116c">"Function.prototype.call was called on which is not a function"</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">)</span><span class="token punctuation" style="color:#393A34">;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">}</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain" style="display:inline-block"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token keyword control-flow" style="color:#00009f">if</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">(</span><span class="token plain">thisArg </span><span class="token operator" style="color:#393A34">===</span><span class="token plain"> </span><span class="token keyword nil" style="color:#00009f">undefined</span><span class="token plain"> </span><span class="token operator" style="color:#393A34">||</span><span class="token plain"> thisArg </span><span class="token operator" style="color:#393A34">===</span><span class="token plain"> </span><span class="token keyword null nil" style="color:#00009f">null</span><span class="token punctuation" style="color:#393A34">)</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">{</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> thisArg </span><span class="token operator" style="color:#393A34">=</span><span class="token plain"> </span><span class="token dom variable" style="color:#36acaa">window</span><span class="token punctuation" style="color:#393A34">;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">}</span><span class="token plain"> </span><span class="token keyword control-flow" style="color:#00009f">else</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">{</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> thisArg </span><span class="token operator" style="color:#393A34">=</span><span class="token plain"> </span><span class="token known-class-name class-name">Object</span><span class="token punctuation" style="color:#393A34">(</span><span class="token plain">thisArg</span><span class="token punctuation" style="color:#393A34">)</span><span class="token punctuation" style="color:#393A34">;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">}</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain" style="display:inline-block"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token comment" style="color:#999988;font-style:italic">// 将 func 放入 thisArg 内，这样在调用 thisArg[func] 时 this 自然就指向了 thisArg</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token keyword" style="color:#00009f">const</span><span class="token plain"> func </span><span class="token operator" style="color:#393A34">=</span><span class="token plain"> </span><span class="token known-class-name class-name">Symbol</span><span class="token punctuation" style="color:#393A34">(</span><span class="token string" style="color:#e3116c">"func"</span><span class="token punctuation" style="color:#393A34">)</span><span class="token punctuation" style="color:#393A34">;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> thisArg</span><span class="token punctuation" style="color:#393A34">[</span><span class="token plain">func</span><span class="token punctuation" style="color:#393A34">]</span><span class="token plain"> </span><span class="token operator" style="color:#393A34">=</span><span class="token plain"> </span><span class="token keyword" style="color:#00009f">this</span><span class="token punctuation" style="color:#393A34">;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain" style="display:inline-block"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token keyword" style="color:#00009f">let</span><span class="token plain"> result</span><span class="token punctuation" style="color:#393A34">;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain" style="display:inline-block"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token keyword control-flow" style="color:#00009f">if</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">(</span><span class="token plain">argsArray</span><span class="token punctuation" style="color:#393A34">.</span><span class="token property-access">length</span><span class="token punctuation" style="color:#393A34">)</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">{</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> result </span><span class="token operator" style="color:#393A34">=</span><span class="token plain"> thisArg</span><span class="token punctuation" style="color:#393A34">[</span><span class="token plain">func</span><span class="token punctuation" style="color:#393A34">]</span><span class="token punctuation" style="color:#393A34">(</span><span class="token spread operator" style="color:#393A34">...</span><span class="token plain">argsArray</span><span class="token punctuation" style="color:#393A34">)</span><span class="token punctuation" style="color:#393A34">;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">}</span><span class="token plain"> </span><span class="token keyword control-flow" style="color:#00009f">else</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">{</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> result </span><span class="token operator" style="color:#393A34">=</span><span class="token plain"> thisArg</span><span class="token punctuation" style="color:#393A34">[</span><span class="token plain">func</span><span class="token punctuation" style="color:#393A34">]</span><span class="token punctuation" style="color:#393A34">(</span><span class="token punctuation" style="color:#393A34">)</span><span class="token punctuation" style="color:#393A34">;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">}</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain" style="display:inline-block"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token keyword" style="color:#00009f">delete</span><span class="token plain"> thisArg</span><span class="token punctuation" style="color:#393A34">[</span><span class="token plain">func</span><span class="token punctuation" style="color:#393A34">]</span><span class="token punctuation" style="color:#393A34">;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain" style="display:inline-block"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token keyword control-flow" style="color:#00009f">return</span><span class="token plain"> result</span><span class="token punctuation" style="color:#393A34">;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"></span><span class="token punctuation" style="color:#393A34">}</span><span class="token punctuation" style="color:#393A34">;</span><br></span></code></pre><div class="buttonGroup__atx"><button type="button" aria-label="Copy code to clipboard" title="Copy" class="clean-btn"><span class="copyButtonIcons_eSgA" aria-hidden="true"><svg class="copyButtonIcon_y97N" viewBox="0 0 24 24"><path d="M19,21H8V7H19M19,5H8A2,2 0 0,0 6,7V21A2,2 0 0,0 8,23H19A2,2 0 0,0 21,21V7A2,2 0 0,0 19,5M16,1H4A2,2 0 0,0 2,3V17H4V3H16V1Z"></path></svg><svg class="copyButtonSuccessIcon_LjdS" viewBox="0 0 24 24"><path d="M21,7L9,19L3.5,13.5L4.91,12.09L9,16.17L19.59,5.59L21,7Z"></path></svg></span></button></div></div></div><h2 class="anchor anchorWithHideOnScrollNavbar_WYt5" id="bind">bind<a href="#bind" class="hash-link" aria-label="Direct link to bind" title="Direct link to bind"></a></h2><h3 class="anchor anchorWithHideOnScrollNavbar_WYt5" id="1-语法-2">1. 语法<a href="#1-语法-2" class="hash-link" aria-label="Direct link to 1. 语法" title="Direct link to 1. 语法"></a></h3><div class="language-jsx codeBlockContainer_Ckt0 theme-code-block" style="--prism-color:#393A34;--prism-background-color:#f6f8fa"><div class="codeBlockContent_biex"><pre tabindex="0" class="prism-code language-jsx codeBlock_bY9V thin-scrollbar"><code class="codeBlockLines_e6Vv"><span class="token-line" style="color:#393A34"><span class="token plain">func</span><span class="token punctuation" style="color:#393A34">.</span><span class="token method function property-access" style="color:#d73a49">bind</span><span class="token punctuation" style="color:#393A34">(</span><span class="token plain">thisArg</span><span class="token punctuation" style="color:#393A34">[</span><span class="token punctuation" style="color:#393A34">,</span><span class="token plain"> arg1</span><span class="token punctuation" style="color:#393A34">[</span><span class="token punctuation" style="color:#393A34">,</span><span class="token plain"> arg2</span><span class="token punctuation" style="color:#393A34">[</span><span class="token punctuation" style="color:#393A34">,</span><span class="token plain"> </span><span class="token spread operator" style="color:#393A34">...</span><span class="token punctuation" style="color:#393A34">]</span><span class="token punctuation" style="color:#393A34">]</span><span class="token punctuation" style="color:#393A34">]</span><span class="token punctuation" style="color:#393A34">)</span><br></span></code></pre><div class="buttonGroup__atx"><button type="button" aria-label="Copy code to clipboard" title="Copy" class="clean-btn"><span class="copyButtonIcons_eSgA" aria-hidden="true"><svg class="copyButtonIcon_y97N" viewBox="0 0 24 24"><path d="M19,21H8V7H19M19,5H8A2,2 0 0,0 6,7V21A2,2 0 0,0 8,23H19A2,2 0 0,0 21,21V7A2,2 0 0,0 19,5M16,1H4A2,2 0 0,0 2,3V17H4V3H16V1Z"></path></svg><svg class="copyButtonSuccessIcon_LjdS" viewBox="0 0 24 24"><path d="M21,7L9,19L3.5,13.5L4.91,12.09L9,16.17L19.59,5.59L21,7Z"></path></svg></span></button></div></div></div><p><strong>参数</strong></p><p><code>thisArg</code></p><p>调用绑定函数时作为 this 参数传递给目标函数的值。 如果使用 new 运算符构造绑定函数，则忽略该值。</p><p><code>arg1, arg2, ...</code></p><p>当目标函数被调用时，被预置入绑定函数的参数列表中的参数。</p><p><strong>返回值</strong></p><p>返回一个原函数的拷贝，并拥有指定的 this 值和初始参数。</p><h3 class="anchor anchorWithHideOnScrollNavbar_WYt5" id="2-流程图-2">2. 流程图<a href="#2-流程图-2" class="hash-link" aria-label="Direct link to 2. 流程图" title="Direct link to 2. 流程图"></a></h3><p><img loading="lazy" src="https://user-images.githubusercontent.com/17525377/147632692-d7d335a7-a236-4bee-85a6-51aedbf285b9.jpg" alt="bind" class="img_ev3q"></p><h3 class="anchor anchorWithHideOnScrollNavbar_WYt5" id="3-编写代码-2">3. 编写代码<a href="#3-编写代码-2" class="hash-link" aria-label="Direct link to 3. 编写代码" title="Direct link to 3. 编写代码"></a></h3><div class="language-jsx codeBlockContainer_Ckt0 theme-code-block" style="--prism-color:#393A34;--prism-background-color:#f6f8fa"><div class="codeBlockContent_biex"><pre tabindex="0" class="prism-code language-jsx codeBlock_bY9V thin-scrollbar"><code class="codeBlockLines_e6Vv"><span class="token-line" style="color:#393A34"><span class="token class-name">Function</span><span class="token punctuation" style="color:#393A34">.</span><span class="token property-access">prototype</span><span class="token punctuation" style="color:#393A34">.</span><span class="token method-variable function-variable method function property-access" style="color:#d73a49">bind</span><span class="token plain"> </span><span class="token operator" style="color:#393A34">=</span><span class="token plain"> </span><span class="token keyword" style="color:#00009f">function</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">(</span><span class="token parameter">thisArg</span><span class="token parameter punctuation" style="color:#393A34">,</span><span class="token parameter"> </span><span class="token parameter spread operator" style="color:#393A34">...</span><span class="token parameter">argsArray</span><span class="token punctuation" style="color:#393A34">)</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">{</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token keyword control-flow" style="color:#00009f">if</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">(</span><span class="token keyword" style="color:#00009f">typeof</span><span class="token plain"> </span><span class="token keyword" style="color:#00009f">this</span><span class="token plain"> </span><span class="token operator" style="color:#393A34">!==</span><span class="token plain"> </span><span class="token string" style="color:#e3116c">"function"</span><span class="token punctuation" style="color:#393A34">)</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">{</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token keyword control-flow" style="color:#00009f">throw</span><span class="token plain"> </span><span class="token keyword" style="color:#00009f">new</span><span class="token plain"> </span><span class="token class-name">TypeError</span><span class="token punctuation" style="color:#393A34">(</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token string" style="color:#e3116c">"Function.prototype.bind was called on which is not a function"</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">)</span><span class="token punctuation" style="color:#393A34">;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">}</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain" style="display:inline-block"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token keyword control-flow" style="color:#00009f">if</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">(</span><span class="token plain">thisArg </span><span class="token operator" style="color:#393A34">===</span><span class="token plain"> </span><span class="token keyword nil" style="color:#00009f">undefined</span><span class="token plain"> </span><span class="token operator" style="color:#393A34">||</span><span class="token plain"> thisArg </span><span class="token operator" style="color:#393A34">===</span><span class="token plain"> </span><span class="token keyword null nil" style="color:#00009f">null</span><span class="token punctuation" style="color:#393A34">)</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">{</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> thisArg </span><span class="token operator" style="color:#393A34">=</span><span class="token plain"> </span><span class="token dom variable" style="color:#36acaa">window</span><span class="token punctuation" style="color:#393A34">;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">}</span><span class="token plain"> </span><span class="token keyword control-flow" style="color:#00009f">else</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">{</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> thisArg </span><span class="token operator" style="color:#393A34">=</span><span class="token plain"> </span><span class="token known-class-name class-name">Object</span><span class="token punctuation" style="color:#393A34">(</span><span class="token plain">thisArg</span><span class="token punctuation" style="color:#393A34">)</span><span class="token punctuation" style="color:#393A34">;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">}</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain" style="display:inline-block"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token keyword" style="color:#00009f">const</span><span class="token plain"> func </span><span class="token operator" style="color:#393A34">=</span><span class="token plain"> </span><span class="token keyword" style="color:#00009f">this</span><span class="token punctuation" style="color:#393A34">;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain" style="display:inline-block"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token keyword" style="color:#00009f">const</span><span class="token plain"> </span><span class="token function-variable function" style="color:#d73a49">bound</span><span class="token plain"> </span><span class="token operator" style="color:#393A34">=</span><span class="token plain"> </span><span class="token keyword" style="color:#00009f">function</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">(</span><span class="token parameter spread operator" style="color:#393A34">...</span><span class="token parameter">boundArgsArray</span><span class="token punctuation" style="color:#393A34">)</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">{</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token keyword" style="color:#00009f">let</span><span class="token plain"> isNew </span><span class="token operator" style="color:#393A34">=</span><span class="token plain"> </span><span class="token boolean" style="color:#36acaa">false</span><span class="token punctuation" style="color:#393A34">;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain" style="display:inline-block"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token comment" style="color:#999988;font-style:italic">// 如果 func 不是构造器，直接使用 instanceof 将出错，所以需要用 try...catch 包裹</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token keyword control-flow" style="color:#00009f">try</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">{</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> isNew </span><span class="token operator" style="color:#393A34">=</span><span class="token plain"> </span><span class="token keyword" style="color:#00009f">this</span><span class="token plain"> </span><span class="token keyword" style="color:#00009f">instanceof</span><span class="token plain"> </span><span class="token class-name">func</span><span class="token punctuation" style="color:#393A34">;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">}</span><span class="token plain"> </span><span class="token keyword control-flow" style="color:#00009f">catch</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">(</span><span class="token plain">error</span><span class="token punctuation" style="color:#393A34">)</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">{</span><span class="token punctuation" style="color:#393A34">}</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain" style="display:inline-block"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token keyword control-flow" style="color:#00009f">return</span><span class="token plain"> func</span><span class="token punctuation" style="color:#393A34">.</span><span class="token method function property-access" style="color:#d73a49">apply</span><span class="token punctuation" style="color:#393A34">(</span><span class="token plain">isNew </span><span class="token operator" style="color:#393A34">?</span><span class="token plain"> </span><span class="token keyword" style="color:#00009f">this</span><span class="token plain"> </span><span class="token operator" style="color:#393A34">:</span><span class="token plain"> thisArg</span><span class="token punctuation" style="color:#393A34">,</span><span class="token plain"> argsArray</span><span class="token punctuation" style="color:#393A34">.</span><span class="token method function property-access" style="color:#d73a49">concat</span><span class="token punctuation" style="color:#393A34">(</span><span class="token plain">boundArgsArray</span><span class="token punctuation" style="color:#393A34">)</span><span class="token punctuation" style="color:#393A34">)</span><span class="token punctuation" style="color:#393A34">;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">}</span><span class="token punctuation" style="color:#393A34">;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain" style="display:inline-block"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token keyword" style="color:#00009f">const</span><span class="token plain"> </span><span class="token function-variable function maybe-class-name" style="color:#d73a49">Empty</span><span class="token plain"> </span><span class="token operator" style="color:#393A34">=</span><span class="token plain"> </span><span class="token keyword" style="color:#00009f">function</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">(</span><span class="token punctuation" style="color:#393A34">)</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">{</span><span class="token punctuation" style="color:#393A34">}</span><span class="token punctuation" style="color:#393A34">;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token class-name">Empty</span><span class="token punctuation" style="color:#393A34">.</span><span class="token property-access">prototype</span><span class="token plain"> </span><span class="token operator" style="color:#393A34">=</span><span class="token plain"> </span><span class="token keyword" style="color:#00009f">this</span><span class="token punctuation" style="color:#393A34">.</span><span class="token property-access">prototype</span><span class="token punctuation" style="color:#393A34">;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> bound</span><span class="token punctuation" style="color:#393A34">.</span><span class="token property-access">prototype</span><span class="token plain"> </span><span class="token operator" style="color:#393A34">=</span><span class="token plain"> </span><span class="token keyword" style="color:#00009f">new</span><span class="token plain"> </span><span class="token class-name">Empty</span><span class="token punctuation" style="color:#393A34">(</span><span class="token punctuation" style="color:#393A34">)</span><span class="token punctuation" style="color:#393A34">;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain" style="display:inline-block"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token keyword control-flow" style="color:#00009f">return</span><span class="token plain"> bound</span><span class="token punctuation" style="color:#393A34">;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"></span><span class="token punctuation" style="color:#393A34">}</span><span class="token punctuation" style="color:#393A34">;</span><br></span></code></pre><div class="buttonGroup__atx"><button type="button" aria-label="Copy code to clipboard" title="Copy" class="clean-btn"><span class="copyButtonIcons_eSgA" aria-hidden="true"><svg class="copyButtonIcon_y97N" viewBox="0 0 24 24"><path d="M19,21H8V7H19M19,5H8A2,2 0 0,0 6,7V21A2,2 0 0,0 8,23H19A2,2 0 0,0 21,21V7A2,2 0 0,0 19,5M16,1H4A2,2 0 0,0 2,3V17H4V3H16V1Z"></path></svg><svg class="copyButtonSuccessIcon_LjdS" viewBox="0 0 24 24"><path d="M21,7L9,19L3.5,13.5L4.91,12.09L9,16.17L19.59,5.59L21,7Z"></path></svg></span></button></div></div></div><h2 class="anchor anchorWithHideOnScrollNavbar_WYt5" id="参考资料">参考资料<a href="#参考资料" class="hash-link" aria-label="Direct link to 参考资料" title="Direct link to 参考资料"></a></h2><ol><li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function/apply" target="_blank" rel="noopener noreferrer">Function.prototype.apply()</a></li><li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function/call" target="_blank" rel="noopener noreferrer">Function.prototype.call()</a></li><li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function/bind" target="_blank" rel="noopener noreferrer">Function.prototype.bind()</a></li></ol></div></article><nav class="pagination-nav docusaurus-mt-lg" aria-label="Docs pages navigation"><a class="pagination-nav__link pagination-nav__link--prev" href="/awesome-interview/book4/css-vertical-horizontal-center"><div class="pagination-nav__sublabel">Previous</div><div class="pagination-nav__label">样式：水平垂直居中方案</div></a><a class="pagination-nav__link pagination-nav__link--next" href="/awesome-interview/book4/array-repeat-number"><div class="pagination-nav__sublabel">Next</div><div class="pagination-nav__label">算法：找到数组中重复的数字</div></a></nav></div></div><div class="col col--3"><div class="tableOfContents_bqdL thin-scrollbar theme-doc-toc-desktop"><ul class="table-of-contents table-of-contents__left-border"><li><a href="#apply" class="table-of-contents__link toc-highlight">apply</a><ul><li><a href="#1-语法" 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