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301 lines
14 KiB
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<article id="wikiArticle">
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<div></div>
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<p><span class="st">运算符的优先级决定了表达式中运算执行的先后顺序</span>，优先级高的运算符最先被执行。</p>
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<div><iframe class="interactive interactive-js" frameborder="0" height="250" src="https://interactive-examples.mdn.mozilla.net/pages/js/expressions-operatorprecedence.html" width="100%"></iframe></div>
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<p class="hidden">The source for this interactive example is stored in a GitHub repository. If you'd like to contribute to the interactive examples project, please clone <a class="external" href="https://github.com/mdn/interactive-examples" rel="noopener">https://github.com/mdn/interactive-examples</a> and send us a pull request.</p>
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<h2 id="Associativity" name="Associativity">结合性</h2>
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<p>结合性决定了拥有相同优先级的运算符的执行顺序。考虑下面这个表达式：</p>
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<pre>a OP b OP c
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</code></pre>
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<p>左结合（左到右）相当于把左边的子表达式加上小括号<code>(a OP b) OP c</code>，右关联（右到左）相当于<code>a OP (b OP c)</code>。赋值运算符是右关联的，所以你可以这么写：</p>
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<pre>a = b = 5;
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</code></pre>
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<p>结果 <code>a</code> 和 <code>b</code> 的值都会成为5。这是因为赋值运算符的返回结果就是赋值运算符右边的那个值，具体过程是：<code>b</code>被赋值为5，然后<code>a</code>也被赋值为 <code>b=5</code> 的返回值，也就是5。</p>
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<h2 id="Table" name="Table">汇总表</h2>
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<p>下面的表将所有运算符按照优先级的不同从高到低排列。</p>
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<table class="fullwidth-table">
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<tbody>
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<tr>
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<th>优先级</th>
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<th>运算类型</th>
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<th>关联性</th>
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<th>运算符</th>
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</tr>
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<tr>
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<td>20</td>
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<td><a href="Reference/Operators/Grouping" title="圆括号运算符( ) 用来控制表达式中的运算优先级。"><code>圆括号</code></a></td>
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<td>n/a</td>
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<td><code>( … )</code></td>
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</tr>
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<tr>
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<td rowspan="4">19</td>
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<td><a href="Reference/Operators/Property_Accessors#点符号表示法" title="属性访问器提供了两种方式用于访问一个对象的属性，它们分别是点号和方括号。"><code>成员访问</code></a></td>
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<td>从左到右</td>
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<td><code>… . …</code></td>
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</tr>
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<tr>
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<td><a href="Reference/Operators/Property_Accessors#括号表示法" title="属性访问器提供了两种方式用于访问一个对象的属性，它们分别是点号和方括号。"><code>需计算的成员访问</code></a></td>
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<td>从左到右</td>
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<td><code>… [ … ]</code></td>
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</tr>
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<tr>
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<td><a href="Reference/Operators/new" title="new 运算符创建一个用户定义的对象类型的实例或具有构造函数的内置对象的实例。"><code>new</code></a> (带参数列表)</td>
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<td>n/a</td>
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<td><code>new … ( … )</code></td>
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</tr>
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<tr>
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<td><a href="https://developer.mozilla.orgGuide/Functions" title="JavaScript/Reference/Operators/Special_Operators/function_call">函数调用</a></td>
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<td>从左到右</td>
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<td><code>… ( <var>… </var>)</code></td>
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</tr>
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<tr>
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<td rowspan="1">18</td>
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<td><a href="https://developer.mozilla.orgReference/Operators/new" title="JavaScript/Reference/Operators/Special_Operators/new_Operator">new</a> (无参数列表)</td>
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<td>从右到左</td>
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<td><code>new …</code></td>
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</tr>
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<tr>
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<td rowspan="2">17</td>
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<td><a href="https://developer.mozilla.orgReference/Operators/Arithmetic_Operators#Increment" title="JavaScript/Reference/Operators/Arithmetic_Operators">后置递增</a>(运算符在后)</td>
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<td colspan="1" rowspan="2">n/a<br/>
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</td>
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<td><code>… ++</code></td>
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</tr>
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<tr>
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<td><a href="https://developer.mozilla.orgReference/Operators/Arithmetic_Operators#Decrement" title="JavaScript/Reference/Operators/Arithmetic_Operators">后置递减</a>(运算符在后)</td>
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<td><code>… --</code></td>
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</tr>
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<tr>
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<td colspan="1" rowspan="10">16</td>
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<td><a href="https://developer.mozilla.orgReference/Operators/Logical_Operators#Logical_NOT">逻辑非</a></td>
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<td colspan="1" rowspan="10">从右到左</td>
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<td><code>! …</code></td>
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</tr>
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<tr>
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<td><a href="https://developer.mozilla.orgReference/Operators/Bitwise_Operators#Bitwise_NOT" title="JavaScript/Reference/Operators/Bitwise_Operators">按位非</a></td>
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<td><code>~ …</code></td>
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</tr>
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<tr>
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<td><a href="https://developer.mozilla.orgReference/Operators/Arithmetic_Operators#Unary_plus" title="JavaScript/Reference/Operators/Arithmetic_Operators">一元加法</a></td>
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<td><code>+ …</code></td>
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</tr>
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<tr>
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<td><a href="https://developer.mozilla.orgReference/Operators/Arithmetic_Operators#Unary_negation" title="JavaScript/Reference/Operators/Arithmetic_Operators">一元减法</a></td>
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<td><code>- …</code></td>
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</tr>
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<tr>
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<td><a href="https://developer.mozilla.orgReference/Operators/Arithmetic_Operators#Increment" title="JavaScript/Reference/Operators/Arithmetic_Operators">前置递增</a></td>
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<td><code>++ …</code></td>
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</tr>
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<tr>
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<td><a href="https://developer.mozilla.orgReference/Operators/Arithmetic_Operators#Decrement" title="JavaScript/Reference/Operators/Arithmetic_Operators">前置递减</a></td>
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<td><code>-- …</code></td>
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</tr>
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<tr>
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<td><a href="https://developer.mozilla.orgReference/Operators/typeof" title="JavaScript/Reference/Operators/Special_Operators/typeof_Operator">typeof</a></td>
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<td><code>typeof …</code></td>
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</tr>
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<tr>
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<td><a href="https://developer.mozilla.orgReference/Operators/void" title="JavaScript/Reference/Operators/Special_Operators/void_Operator">void</a></td>
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<td><code>void …</code></td>
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</tr>
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<tr>
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<td><a href="https://developer.mozilla.orgReference/Operators/delete" title="JavaScript/Reference/Operators/Special_Operators/delete_Operator">delete</a></td>
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<td><code>delete …</code></td>
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</tr>
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<tr>
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<td><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/await">await</a></td>
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<td><code>await …</code></td>
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</tr>
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<tr>
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<td>15</td>
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<td><a href="https://developer.mozilla.orgReference/Operators/Arithmetic_Operators#Exponentiation" title="JavaScript/Reference/Operators/Arithmetic_Operators">幂</a></td>
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<td>从右到左</td>
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<td><code>… ** …</code></td>
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</tr>
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<tr>
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<td rowspan="3">14</td>
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<td><a href="https://developer.mozilla.orgReference/Operators/Arithmetic_Operators#Multiplication" title="JavaScript/Reference/Operators/Arithmetic_Operators">乘法</a></td>
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<td colspan="1" rowspan="3">从左到右<br/>
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</td>
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<td><code>… * …</code></td>
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</tr>
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<tr>
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<td><a href="https://developer.mozilla.orgReference/Operators/Arithmetic_Operators#Division" title="JavaScript/Reference/Operators/Arithmetic_Operators">除法</a></td>
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<td><code>… / …</code></td>
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</tr>
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<tr>
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<td><a href="https://developer.mozilla.orgReference/Operators/Arithmetic_Operators#Remainder" title="JavaScript/Reference/Operators/Arithmetic_Operators">取模</a></td>
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<td><code>… % …</code></td>
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</tr>
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<tr>
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<td rowspan="2">13</td>
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<td><a href="https://developer.mozilla.orgReference/Operators/Arithmetic_Operators#Addition" title="JavaScript/Reference/Operators/Arithmetic_Operators">加法</a></td>
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<td colspan="1" rowspan="2">从左到右<br/>
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</td>
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<td><code>… + …</code></td>
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</tr>
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<tr>
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<td><a href="https://developer.mozilla.orgReference/Operators/Arithmetic_Operators#Subtraction" title="JavaScript/Reference/Operators/Arithmetic_Operators">减法</a></td>
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<td><code>… - …</code></td>
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</tr>
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<tr>
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<td rowspan="3">12</td>
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<td><a href="https://developer.mozilla.orgReference/Operators/Bitwise_Operators" title="JavaScript/Reference/Operators/Bitwise_Operators">按位左移</a></td>
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<td colspan="1" rowspan="3">从左到右</td>
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<td><code>… << …</code></td>
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</tr>
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<tr>
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<td><a href="https://developer.mozilla.orgReference/Operators/Bitwise_Operators" title="JavaScript/Reference/Operators/Bitwise_Operators">按位右移</a></td>
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<td><code>… >> …</code></td>
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</tr>
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<tr>
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<td><a href="https://developer.mozilla.orgReference/Operators/Bitwise_Operators" title="JavaScript/Reference/Operators/Bitwise_Operators">无符号右移</a></td>
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<td><code>… >>> …</code></td>
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</tr>
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<tr>
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<td rowspan="6">11</td>
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<td><a href="https://developer.mozilla.orgReference/Operators/Comparison_Operators#Less_than_operator" title="JavaScript/Reference/Operators/Comparison_Operators">小于</a></td>
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<td colspan="1" rowspan="6">从左到右</td>
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<td><code>… < …</code></td>
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</tr>
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<tr>
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<td><a href="https://developer.mozilla.orgReference/Operators/Comparison_Operators#Less_than__or_equal_operator" title="JavaScript/Reference/Operators/Comparison_Operators">小于等于</a></td>
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<td><code>… <= …</code></td>
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</tr>
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<tr>
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<td><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Comparison_Operators#Greater_than_operator" title="JavaScript/Reference/Operators/Comparison_Operators">大于</a></td>
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<td><code>… > …</code></td>
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</tr>
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<tr>
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<td><a href="https://developer.mozilla.orgReference/Operators/Comparison_Operators#Greater_than_or_equal_operator" title="JavaScript/Reference/Operators/Comparison_Operators">大于等于</a></td>
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<td><code>… >= …</code></td>
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</tr>
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<tr>
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<td><a href="https://developer.mozilla.orgReference/Operators/in" title="JavaScript/Reference/Operators/Special_Operators/in_Operator">in</a></td>
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<td><code>… in …</code></td>
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</tr>
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<tr>
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<td><a href="https://developer.mozilla.orgReference/Operators/instanceof" title="JavaScript/Reference/Operators/Special_Operators/instanceof_Operator">instanceof</a></td>
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<td><code>… instanceof …</code></td>
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</tr>
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<tr>
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<td rowspan="4">10</td>
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<td><a href="https://developer.mozilla.orgReference/Operators/Comparison_Operators#Equality" title="JavaScript/Reference/Operators/Comparison_Operators">等号</a></td>
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<td colspan="1" rowspan="4">从左到右<br/>
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</td>
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<td><code>… == …</code></td>
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</tr>
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<tr>
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<td><a href="https://developer.mozilla.orgReference/Operators/Comparison_Operators#Inequality" title="JavaScript/Reference/Operators/Comparison_Operators">非等号</a></td>
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<td><code>… != …</code></td>
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</tr>
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<tr>
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<td><a href="https://developer.mozilla.orgReference/Operators/Comparison_Operators#Identity" title="JavaScript/Reference/Operators/Comparison_Operators">全等号</a></td>
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<td><code>… === …</code></td>
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</tr>
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<tr>
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<td><a href="https://developer.mozilla.orgReference/Operators/Comparison_Operators#Nonidentity" title="JavaScript/Reference/Operators/Comparison_Operators">非全等号</a></td>
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<td><code>… !== …</code></td>
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</tr>
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<tr>
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<td>9</td>
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<td><a href="https://developer.mozilla.orgReference/Operators/Bitwise_Operators#Bitwise_AND" title="JavaScript/Reference/Operators/Bitwise_Operators">按位与</a></td>
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<td>从左到右</td>
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<td><code>… & …</code></td>
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</tr>
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<tr>
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<td>8</td>
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<td><a href="https://developer.mozilla.orgReference/Operators/Bitwise_Operators#Bitwise_XOR" title="JavaScript/Reference/Operators/Bitwise_Operators">按位异或</a></td>
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<td>从左到右</td>
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<td><code>… ^ …</code></td>
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</tr>
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<tr>
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<td>7</td>
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<td><a href="https://developer.mozilla.orgReference/Operators/Bitwise_Operators#Bitwise_OR" title="JavaScript/Reference/Operators/Bitwise_Operators">按位或</a></td>
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<td>从左到右</td>
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<td><code>… | …</code></td>
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</tr>
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<tr>
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<td>6</td>
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<td><a href="https://developer.mozilla.orgReference/Operators/Logical_Operators#Logical_AND" title="JavaScript/Reference/Operators/Logical_Operators">逻辑与</a></td>
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<td>从左到右</td>
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<td><code>… && …</code></td>
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</tr>
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<tr>
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<td>5</td>
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<td><a href="https://developer.mozilla.orgReference/Operators/Logical_Operators#Logical_OR" title="JavaScript/Reference/Operators/Logical_Operators">逻辑或</a></td>
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<td>从左到右</td>
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<td><code>… || …</code></td>
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</tr>
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<tr>
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<td>4</td>
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<td><a href="https://developer.mozilla.orgReference/Operators/Conditional_Operator" title="JavaScript/Reference/Operators/Special_Operators/Conditional_Operator">条件运算符</a></td>
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<td>从右到左</td>
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<td><code>… ? … : …</code></td>
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</tr>
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<tr>
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<td rowspan="12">3</td>
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<td rowspan="12"><a href="https://developer.mozilla.orgReference/Operators/Assignment_Operators" title="JavaScript/Reference/Operators/Assignment_Operators">赋值</a></td>
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<td rowspan="12">从右到左</td>
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<td><code>… = …</code></td>
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</tr>
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<tr>
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<td><code>… += …</code></td>
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</tr>
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<tr>
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<td><code>… -= …</code></td>
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</tr>
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<tr>
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<td><code>… *= …</code></td>
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</tr>
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<tr>
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<td><code>… /= …</code></td>
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</tr>
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<tr>
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<td><code>… %= …</code></td>
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</tr>
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<tr>
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<td><code>… <<= …</code></td>
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</tr>
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<tr>
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<td><code>… >>= …</code></td>
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</tr>
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<tr>
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<td><code>… >>>= …</code></td>
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</tr>
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<tr>
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<td><code>… &= …</code></td>
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</tr>
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<tr>
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<td><code>… ^= …</code></td>
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</tr>
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<tr>
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<td><code>… |= …</code></td>
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</tr>
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<tr>
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<td colspan="1" rowspan="2">2</td>
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<td><a href="https://developer.mozilla.orgReference/Operators/yield" title="JavaScript/Reference/Operators/yield">yield</a></td>
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<td colspan="1" rowspan="2">从右到左</td>
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<td><code>yield …</code></td>
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</tr>
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<tr>
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<td><a href="https://developer.mozilla.orgReference/Operators/yield*" title="JavaScript/Reference/Operators/yield">yield*</a></td>
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<td><code>yield* …</code></td>
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</tr>
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<tr>
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<td>1</td>
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<td><a href="https://developer.mozilla.orgReference/Operators/Spread_operator" title="JavaScript/Reference/Operators/Spread_operator">展开运算符</a></td>
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<td>n/a</td>
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<td><code>...</code> …</td>
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</tr>
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<tr>
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<td>0</td>
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<td><a href="https://developer.mozilla.orgReference/Operators/Comma_Operator" title="JavaScript/Reference/Operators/Comma_Operator">逗号</a></td>
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<td>从左到右</td>
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<td><code>… , …</code></td>
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</tr>
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</tbody>
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</table>
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<p> </p>
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</article> |