运算符——JavaScript

Posted zealifree005

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　　一.什么是表达式

　　表达式是ECMAScript中的一个“短语”，解析器会通过计算把它转换成一个值。最简单的表达式是字面量或者变量名。例如：

<code class="hljs javascript has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">5.96</span>                            <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//数值字面量</span>
<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">'Lee'</span>                           <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//字符串字面量</span>
<span class="hljs-literal" style="color: rgb(0, 102, 102); box-sizing: border-box;">true</span>                            <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//布尔值字面量    </span>
<span class="hljs-literal" style="color: rgb(0, 102, 102); box-sizing: border-box;">null</span>                            <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//空值字面量</span>
/Java/                          <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//正则表达式字面量</span>
x:<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span>, y:<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">2</span>                      <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//对象字面量、对象表达式</span>
[<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span>,<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">2</span>,<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">3</span>]                         <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//数组字面量、数组表达式</span>
<span class="hljs-function" style="box-sizing: border-box;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">function</span><span class="hljs-params" style="color: rgb(102, 0, 102); box-sizing: border-box;">(n)</span> </span><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> x+y;       <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//函数字面量、函数表达式</span>
box                             <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//变量</span>
</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li></ul>

  • 通过合并简单的表达式来创建复杂的表达式。比如：
<code class="hljs cs has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;">box + <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">5.96</span>                      <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//加法运算的表达式</span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">typeof</span>(box)                     <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//查看数据类型的表达式</span>
box > <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">8</span>                         <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//逻辑运算表达式</span>
</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li></ul>
  • 单一的字面量和组合字面量的运算符都可称为表达式

　　二.一元运算符

　　只能操作一个值的运算符叫做一元运算符

　　1.递增++和递减–

　　2.前置和后置的区别

　　没有赋值操作，前置和后置是一样的

　　有赋值操作时

　　前置的运算符会先累加(累减)再赋值

　　后置运算符则先赋值再累加或累减

  • <code class="hljs cs has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">var</span> box = <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">100</span>; 
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">var</span> age = ++box;                   <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//age值为101</span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">var</span> height = box++;            <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//height值为100</span>
</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li></ul>

    • 3.其他类型应用一元运算符的规则

      <code class="hljs javascript has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">var</span> box = <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">'89'</span>;    box++;           <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//90，数值字符串自动转换成数值</span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">var</span> box = <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">'ab'</span>; box++;           <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//NaN，字符串包含非数值转成NaN</span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">var</span> box = <span class="hljs-literal" style="color: rgb(0, 102, 102); box-sizing: border-box;">false</span>; box++;          <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//1，false转成数值是0，累加就是1</span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">var</span> box = <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">2.3</span>; box++;            <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//3.3，直接加1</span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">var</span> box =                           <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//1，不设置toString或valueOf即为NaN</span>
toString : <span class="hljs-function" style="box-sizing: border-box;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">function</span><span class="hljs-params" style="color: rgb(102, 0, 102); box-sizing: border-box;">()</span> </span>
    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span>;

;          box++;
</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li></ul>

    • 4.加和减运算符

      <code class="hljs javascript has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">var</span> box = <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">100</span>; +box;                <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//100，对于数值，不会产生任何影响</span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">var</span> box = <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">'89'</span>; +box;               <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//89，数值字符串转换成数值</span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">var</span> box = <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">'ab'</span>; +box;               <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//NaN，字符串包含非数值转成NaN</span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">var</span> box = <span class="hljs-literal" style="color: rgb(0, 102, 102); box-sizing: border-box;">false</span>; +box;          <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//0，布尔值转换成相应数值</span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">var</span> box = <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">2.3</span>; +box;                <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//2.3，没有变化</span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">var</span> box =                      <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//1，不设置toString或valueOf即为NaN</span>
toString : <span class="hljs-function" style="box-sizing: border-box;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">function</span><span class="hljs-params" style="color: rgb(102, 0, 102); box-sizing: border-box;">()</span> </span>
    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span>;

;          +box;
</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li></ul>

三．算术运算符

  • 1.加法
<code class="hljs javascript has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">var</span> box = <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span> + <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">2</span>;                    <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//等于3</span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">var</span> box = <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span> + <span class="hljs-literal" style="color: rgb(0, 102, 102); box-sizing: border-box;">NaN</span>;                  <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//NaN，只要有一个NaN就为NaN</span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">var</span> box = <span class="hljs-literal" style="color: rgb(0, 102, 102); box-sizing: border-box;">Infinity</span> + <span class="hljs-literal" style="color: rgb(0, 102, 102); box-sizing: border-box;">Infinity</span>;      <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//Infinity</span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">var</span> box = -<span class="hljs-literal" style="color: rgb(0, 102, 102); box-sizing: border-box;">Infinity</span> + -<span class="hljs-literal" style="color: rgb(0, 102, 102); box-sizing: border-box;">Infinity</span>;    <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//-Infinity</span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">var</span> box = <span class="hljs-literal" style="color: rgb(0, 102, 102); box-sizing: border-box;">Infinity</span> + -<span class="hljs-literal" style="color: rgb(0, 102, 102); box-sizing: border-box;">Infinity</span>;     <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//NaN，正无穷和负无穷相加等NaN</span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">var</span> box = <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">100</span> + <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">'100'</span>;              <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//100100，字符串连接符，有字符串就不是加法</span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">var</span> box = <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">'您的年龄是：'</span> + <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">10</span> + <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">20</span>;   <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//您的年龄是：1020，被转换成字符串</span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">var</span> box = <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">10</span> + <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">20</span> + <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">'是您的年龄'</span>;        <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//30是您的年龄，没有被转成字符串</span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">var</span> box = <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">'您的年龄是：'</span> + (<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">10</span> + <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">20</span>); <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//您的年龄是：30，没有被转成字符串</span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">var</span> box = <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">10</span> + ；             <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//10[object Object]类型是string</span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">var</span> box = <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">10</span> + 对象               <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//10[object Object]，如果有toString()或valueOf()，则返回10+返回数的值</span>
</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li></ul>
  • 2.减法
<code class="hljs javascript has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">var</span> box = <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">100</span> - <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">70</span>;                 <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//等于30</span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">var</span> box = -<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">100</span> - <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">70</span>                 <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//等于-170</span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">var</span> box = -<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">100</span> - -<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">70</span>                <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//-30，一般写成-100 - (-70)比较清晰</span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">var</span> box = <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span> - <span class="hljs-literal" style="color: rgb(0, 102, 102); box-sizing: border-box;">NaN</span>;                  <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//NaN，只要有一个NaN就为NaN</span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">var</span> box = <span class="hljs-literal" style="color: rgb(0, 102, 102); box-sizing: border-box;">Infinity</span> - <span class="hljs-literal" style="color: rgb(0, 102, 102); box-sizing: border-box;">Infinity</span>;          <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//NaN</span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">var</span> box = -<span class="hljs-literal" style="color: rgb(0, 102, 102); box-sizing: border-box;">Infinity</span> - -<span class="hljs-literal" style="color: rgb(0, 102, 102); box-sizing: border-box;">Infinity</span>;        <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//NaN</span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">var</span> box = <span class="hljs-literal" style="color: rgb(0, 102, 102); box-sizing: border-box;">Infinity</span> - -<span class="hljs-literal" style="color: rgb(0, 102, 102); box-sizing: border-box;">Infinity</span>;         <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//Infinity</span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">var</span> box = -<span class="hljs-literal" style="color: rgb(0, 102, 102); box-sizing: border-box;">Infinity</span> - <span class="hljs-literal" style="color: rgb(0, 102, 102); box-sizing: border-box;">Infinity</span>;         <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//-Infinity</span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">var</span> box = <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">100</span> - <span class="hljs-literal" style="color: rgb(0, 102, 102); box-sizing: border-box;">true</span>;               <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//99，true转成数值为1</span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">var</span> box = <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">100</span> - <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">''</span>;                 <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//100，''转成了0</span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">var</span> box = <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">100</span> - <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">'70'</span>;               <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//30，'70'转成了数值70</span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">var</span> box = <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">100</span> - <span class="hljs-literal" style="color: rgb(0, 102, 102); box-sizing: border-box;">null</span>;               <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//100，null转成了0</span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">var</span> box = <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">100</span> - <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">'Lee'</span>;              <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//NaN，Lee转成了NaN</span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">var</span> box = <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">100</span> - 对象              <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//NaN，如果有toString()或valueOf()</span>
 则返回<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">10</span>-返回数的值
</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li></ul>
  • 3.乘法
<code class="hljs javascript has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">var</span> box = <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">100</span> * <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">70</span>;                 <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//7000          </span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">var</span> box = <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">100</span> * <span class="hljs-literal" style="color: rgb(0, 102, 102); box-sizing: border-box;">NaN</span>;                <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//NaN，只要有一个NaN即为NaN</span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">var</span> box = <span class="hljs-literal" style="color: rgb(0, 102, 102); box-sizing: border-box;">Infinity</span> * <span class="hljs-literal" style="color: rgb(0, 102, 102); box-sizing: border-box;">Infinity</span>;          <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//Infinity</span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">var</span> box = -<span class="hljs-literal" style="color: rgb(0, 102, 102); box-sizing: border-box;">Infinity</span> * <span class="hljs-literal" style="color: rgb(0, 102, 102); box-sizing: border-box;">Infinity</span> ;        <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//-Infinity</span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">var</span> box = -<span class="hljs-literal" style="color: rgb(0, 102, 102); box-sizing: border-box;">Infinity</span> * -<span class="hljs-literal" style="color: rgb(0, 102, 102); box-sizing: border-box;">Infinity</span> ;       <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//Infinity</span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">var</span> box = <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">100</span> * <span class="hljs-literal" style="color: rgb(0, 102, 102); box-sizing: border-box;">true</span>;               <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//100，true转成数值为1</span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">var</span> box = <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">100</span> * <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">''</span>;                 <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//0，''转成了0</span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">var</span> box = <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">100</span> * <span class="hljs-literal" style="color: rgb(0, 102, 102); box-sizing: border-box;">null</span>;               <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//0，null转成了0</span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">var</span> box = <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">100</span> * <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">'Lee'</span>;              <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//NaN，Lee转成了NaN</span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">var</span> box = <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">100</span> * 对象              <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//NaN，如果有toString()或valueOf()</span>
 则返回<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">10</span> - 返回数的值</code>

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