# js中push pop unshift shift的區別 ``` <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> 　　這兩組同為對數組的操作，并且會改變數組的本身的長度及內容。 <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">是從數組的尾部進行增減，unshift</span><span class="token1">(</span><span class="token1">)</span><span class="token3">、shift</span><span class="token1">(</span><span class="token1">)</span> 是從數組的頭部進行增減。 <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> 　　向數組的 尾部<span class="token">/</span>頭部 <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 數組的 <span class="token">**</span>新長度<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 的新長度 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 的新長度 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> 　　從數組的 尾部<span class="token">/</span>頭部<span class="token">**</span><span class="token">*</span><span class="token3">刪除1個元素</span><span class="token1">(</span>刪且只刪除<span class="token5">1</span>個<span class="token1">)</span><span class="token">**</span><span class="token">*</span>，并返回<span class="token">**</span>被刪除的元素<span class="token">**</span>；空數組是繼續刪除，不報錯，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> 不接受傳參，即使傳了參數也沒什么卵用<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；**永遠返回最后一個；**</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; **永遠返回第一個；**</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 = \[\];