manual-javascript
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JavaScript 是一种具有函数优先的轻量级、解释型、即时编译型的编程语言。
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<h1 id="函数功能">函数功能</h1>
<p>执行下面的代码，定义并调用指定函数。</p>
<pre class="language-"><code class="lang-javascript"><span class="token keyword">function</span> <span class="token function">func</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
<span class="token keyword">return</span> <span class="token number">233</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>
console<span class="token punctuation">.</span><span class="token function">log</span><span class="token punctuation">(</span><span class="token function">func</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
</code></pre>
<p>执行下面的代码，计算两个整数之和。</p>
<pre class="language-"><code class="lang-javascript"><span class="token keyword">function</span> <span class="token function">sum</span><span class="token punctuation">(</span><span class="token parameter">x<span class="token punctuation">,</span> y</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
<span class="token keyword">return</span> x <span class="token operator">+</span> y<span class="token punctuation">;</span>
<span class="token punctuation">}</span>
console<span class="token punctuation">.</span><span class="token function">log</span><span class="token punctuation">(</span><span class="token function">sum</span><span class="token punctuation">(</span><span class="token number">233</span><span class="token punctuation">,</span> <span class="token number">666</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
</code></pre>
<p>执行下面的代码，为函数指定默认参数。</p>
<pre class="language-"><code class="lang-javascript"><span class="token keyword">function</span> <span class="token function">sum</span><span class="token punctuation">(</span><span class="token parameter">x <span class="token operator">=</span> <span class="token number">0</span><span class="token punctuation">,</span> y <span class="token operator">=</span> <span class="token number">0</span></span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
<span class="token keyword">return</span> x <span class="token operator">+</span> y<span class="token punctuation">;</span>
<span class="token punctuation">}</span>
console<span class="token punctuation">.</span><span class="token function">log</span><span class="token punctuation">(</span><span class="token function">sum</span><span class="token punctuation">(</span><span class="token number">233</span><span class="token punctuation">,</span> <span class="token number">666</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
console<span class="token punctuation">.</span><span class="token function">log</span><span class="token punctuation">(</span><span class="token function">sum</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
</code></pre>
<p>执行下面的代码，获取函数的剩余参数。</p>
<pre class="language-"><code class="lang-javascript"><span class="token keyword">function</span> <span class="token function">func1</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
console<span class="token punctuation">.</span><span class="token function">log</span><span class="token punctuation">(</span>arguments<span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>
<span class="token function">func1</span><span class="token punctuation">(</span><span class="token number">1</span><span class="token punctuation">,</span> <span class="token number">2</span><span class="token punctuation">,</span> <span class="token number">3</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token keyword">function</span> <span class="token function">func2</span><span class="token punctuation">(</span><span class="token parameter"><span class="token operator">...</span>args</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
console<span class="token punctuation">.</span><span class="token function">log</span><span class="token punctuation">(</span>args<span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>
<span class="token function">func2</span><span class="token punctuation">(</span><span class="token number">1</span><span class="token punctuation">,</span> <span class="token number">2</span><span class="token punctuation">,</span> <span class="token number">3</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
</code></pre>
<p>执行下面的代码，定义并调用匿名函数。</p>
<pre class="language-"><code class="lang-javascript"><span class="token keyword">let</span> <span class="token function-variable function">func1</span> <span class="token operator">=</span> <span class="token keyword">function</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
<span class="token keyword">return</span> <span class="token number">233</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>
<span class="token keyword">let</span> <span class="token function-variable function">func2</span> <span class="token operator">=</span> <span class="token keyword">function</span><span class="token punctuation">(</span><span class="token parameter">x<span class="token punctuation">,</span> y</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
<span class="token keyword">return</span> x <span class="token operator">+</span> y<span class="token punctuation">;</span>
<span class="token punctuation">}</span>
console<span class="token punctuation">.</span><span class="token function">log</span><span class="token punctuation">(</span><span class="token function">func1</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
console<span class="token punctuation">.</span><span class="token function">log</span><span class="token punctuation">(</span><span class="token function">func2</span><span class="token punctuation">(</span><span class="token number">233</span><span class="token punctuation">,</span> <span class="token number">666</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
</code></pre>
<p>执行下面的代码，定义并调用立即执行函数。</p>
<pre class="language-"><code class="lang-javascript"><span class="token punctuation">(</span><span class="token keyword">function</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
console<span class="token punctuation">.</span><span class="token function">log</span><span class="token punctuation">(</span><span class="token string">'Hello World!'</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span><span class="token punctuation">)</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">(</span><span class="token keyword">function</span><span class="token punctuation">(</span><span class="token parameter">x<span class="token punctuation">,</span> y</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
console<span class="token punctuation">.</span><span class="token function">log</span><span class="token punctuation">(</span>x <span class="token operator">+</span> y<span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span><span class="token punctuation">)</span><span class="token punctuation">(</span><span class="token number">233</span><span class="token punctuation">,</span> <span class="token number">666</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
</code></pre>
<p>执行下面的代码，定义并调用定时器函数。</p>
<pre class="language-"><code class="lang-javascript"><span class="token keyword">let</span> timer1 <span class="token operator">=</span> <span class="token function">setTimeout</span><span class="token punctuation">(</span><span class="token keyword">function</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
console<span class="token punctuation">.</span><span class="token function">log</span><span class="token punctuation">(</span><span class="token string">'Hello World!'</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span><span class="token punctuation">,</span> <span class="token number">3000</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token keyword">let</span> timer2 <span class="token operator">=</span> <span class="token function">setInterval</span><span class="token punctuation">(</span><span class="token keyword">function</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
console<span class="token punctuation">.</span><span class="token function">log</span><span class="token punctuation">(</span><span class="token string">'Hello JavaScript!'</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span><span class="token punctuation">,</span> <span class="token number">3000</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token keyword">function</span> <span class="token function">func</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
console<span class="token punctuation">.</span><span class="token function">log</span><span class="token punctuation">(</span><span class="token number">233</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>
<span class="token keyword">let</span> timer3 <span class="token operator">=</span> <span class="token function">setInterval</span><span class="token punctuation">(</span>func<span class="token punctuation">,</span> <span class="token number">3000</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
</code></pre>
<p>执行下面的代码，定义并调用闭包函数。</p>
<pre class="language-"><code class="lang-javascript"><span class="token keyword">function</span> <span class="token function">outer</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
<span class="token keyword">let</span> num <span class="token operator">=</span> <span class="token number">233</span><span class="token punctuation">;</span>
<span class="token keyword">function</span> <span class="token function">inner</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
console<span class="token punctuation">.</span><span class="token function">log</span><span class="token punctuation">(</span>num<span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>
<span class="token keyword">return</span> inner<span class="token punctuation">;</span>
<span class="token punctuation">}</span>
<span class="token keyword">const</span> func <span class="token operator">=</span> <span class="token function">outer</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token function">func</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
</code></pre>
<p>执行下面的代码，定义并调用箭头函数。</p>
<pre class="language-"><code class="lang-javascript"><span class="token keyword">const</span> <span class="token function-variable function">func1</span> <span class="token operator">=</span> <span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token operator">=></span> <span class="token punctuation">{</span>
console<span class="token punctuation">.</span><span class="token function">log</span><span class="token punctuation">(</span><span class="token string">'Hello World!'</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>
<span class="token function">func1</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token keyword">const</span> <span class="token function-variable function">func2</span> <span class="token operator">=</span> <span class="token parameter">num</span> <span class="token operator">=></span> <span class="token punctuation">{</span>
console<span class="token punctuation">.</span><span class="token function">log</span><span class="token punctuation">(</span>num<span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>
<span class="token function">func2</span><span class="token punctuation">(</span><span class="token number">233</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token keyword">const</span> <span class="token function-variable function">func3</span> <span class="token operator">=</span> <span class="token parameter">num</span> <span class="token operator">=></span> console<span class="token punctuation">.</span><span class="token function">log</span><span class="token punctuation">(</span>num<span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token function">func3</span><span class="token punctuation">(</span><span class="token number">666</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token keyword">const</span> <span class="token function-variable function">func4</span> <span class="token operator">=</span> <span class="token parameter">num</span> <span class="token operator">=></span> num <span class="token operator">*</span> <span class="token number">2</span><span class="token punctuation">;</span>
console<span class="token punctuation">.</span><span class="token function">log</span><span class="token punctuation">(</span><span class="token function">func4</span><span class="token punctuation">(</span><span class="token number">1.23</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
</code></pre>
<p>执行下面的代码，定义并调用生成器函数。</p>
<pre class="language-"><code class="lang-javascript"><span class="token keyword">function</span><span class="token operator">*</span> <span class="token function">func</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
<span class="token keyword">yield</span> <span class="token number">1</span><span class="token punctuation">;</span>
<span class="token keyword">yield</span> <span class="token number">2</span><span class="token punctuation">;</span>
<span class="token keyword">yield</span> <span class="token number">3</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>
<span class="token keyword">for</span> <span class="token punctuation">(</span><span class="token keyword">let</span> v <span class="token keyword">of</span> <span class="token function">func</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
console<span class="token punctuation">.</span><span class="token function">log</span><span class="token punctuation">(</span>v<span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>
</code></pre>
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