# js中push pop unshift shift的区别 ``` <pre class="calibre29">``` <span class="token5">1</span><span class="token3">、push</span><span class="token1">(</span><span class="token1">)</span><span class="token3">、pop</span><span class="token1">(</span><span class="token1">)</span><span class="token3">和unshift</span><span class="token1">(</span><span class="token1">)</span><span class="token3">、shift</span><span class="token1">(</span><span class="token1">)</span> 　　这两组同为对数组的操作，并且会改变数组的本身的长度及内容。 <span class="token3">　　不同的是 push</span><span class="token1">(</span><span class="token1">)</span><span class="token3">、pop</span><span class="token1">(</span><span class="token1">)</span> <span class="token3">是从数组的尾部进行增减，unshift</span><span class="token1">(</span><span class="token1">)</span><span class="token3">、shift</span><span class="token1">(</span><span class="token1">)</span> 是从数组的头部进行增减。 <span class="token2">var</span> <span><span class="token4">`arr = [1,2];`</span></span> <span class="token5">2</span><span class="token3">、push</span><span class="token1">(</span><span class="token1">)</span><span class="token3">和unshift</span><span class="token1">(</span><span class="token1">)</span> 　　向数组的 尾部<span class="token">/</span>头部 <span class="token">**</span><span class="token">*</span>添加若干元素<span class="token">**</span><span class="token">*</span>，并返回 数组的 <span class="token">**</span>新长度<span class="token">**</span>； 　　arr<span class="token1">.</span><span class="token3">push</span><span class="token1">(</span><span class="token5">3</span><span class="token1">,</span><span class="token5">4</span><span class="token1">)</span>； <span class="token6">//返回 arr 的新长度 4</span> 　　arr <span class="token1">;</span> <span class="token6">// arr = \[1,2,3,4\];</span> 　　arr<span class="token1">.</span><span class="token3">unshift</span><span class="token1">(</span><span class="token5">0</span><span class="token1">,</span><span class="token5">0.5</span><span class="token1">)</span><span class="token1">;</span> <span class="token6">// 返回 arr 的新长度 6</span> 　　arr <span class="token1">;</span> <span class="token6">// arr = \[0,0.5,1,2,3,4\];</span> <span class="token5">3</span><span class="token3">、pop</span><span class="token1">(</span><span class="token1">)</span><span class="token3">和shift</span><span class="token1">(</span><span class="token1">)</span> 　　从数组的 尾部<span class="token">/</span>头部<span class="token">**</span><span class="token">*</span><span class="token3">删除1个元素</span><span class="token1">(</span>删且只删除<span class="token5">1</span>个<span class="token1">)</span><span class="token">**</span><span class="token">*</span>，并返回<span class="token">**</span>被删除的元素<span class="token">**</span>；空数组是继续删除，不报错，但返回undefined； 　　arr<span class="token1">.</span><span class="token3">pop</span><span class="token1">(</span><span class="token1">)</span><span class="token1">;</span>　　　　　　<span class="token6">//返回 4；</span> 　　arr <span class="token1">;</span>　　　　　　　　 <span class="token6">// arr = \[0,0.5,1,2,3\];</span> 　　arr<span class="token1">.</span><span class="token3">pop</span><span class="token1">(</span><span class="token1">)</span><span class="token1">;</span>　　　　　　<span class="token6">//返回 3；</span> 　　arr <span class="token1">;</span>　　　　　　　　 <span class="token6">// arr = \[0,0.5,1,2\];</span> 　　arr<span class="token1">.</span><span class="token3">shift</span><span class="token1">(</span><span class="token1">)</span>；　　　　 <span class="token6">// 返回 0 ；</span> 　　arr <span class="token1">;</span>　　　　　　　　<span class="token6">// arr = \[0.5,1,2\]</span> 　　<span class="token">**</span><span class="token5">PS</span><span class="token1">:</span><span class="token">**</span><span class="token3"> pop</span><span class="token1">(</span><span class="token1">)</span><span class="token3">和shift</span><span class="token1">(</span><span class="token1">)</span> 不接受传参，即使传了参数也没什么卵用<span class="token">~</span><span class="token">~</span>； 　　arr<span class="token1">.</span><span class="token3">pop</span><span class="token1">(</span><span class="token5">3</span><span class="token1">)</span> <span class="token1">;</span> <span class="token6">// 返回 2；**永远返回最后一个；**</span> 　　arr <span class="token1">;</span> 　　　　　　　<span class="token6">// arr = \[0.5,1\];</span> 　　arr<span class="token1">.</span><span class="token3">shift</span><span class="token1">(</span><span class="token5">1</span><span class="token1">)</span><span class="token1">;</span>　　　　<span class="token6">// 返回 0.5; **永远返回第一个；**</span> 　　arr <span class="token1">;</span>　　　　　　　　<span class="token6">// arr = \[1\];</span> 　　arr<span class="token1">.</span><span class="token3">pop</span><span class="token1">(</span><span class="token1">)</span> <span class="token1">;</span> 　　　　<span class="token6">// 返回 1；</span> 　　arr <span class="token1">;</span>　　　　　　　　<span class="token6">// arr = \[\];</span> 　　arr<span class="token1">.</span><span class="token3">shift</span><span class="token1">(</span><span class="token1">)</span>　　　　　<span class="token6">// 返回 undefined；</span> ``` ``` arr ; // arr = \[\];