標籤：返回 rip htm 基礎 var size blog ext efi
1 <!DOCTYPE html> 2 <html> 3 <head> 4 <meta charset="UTF-8"> 5 <title></title> 6 <script type="text/javascript"> 7 8 /* 9 * Null（空值）類型的值只有一個，就是null10 * null這個值專門用來表示一個為空白的對象11 * 使用typeof檢查一個null值時，會返回object12 * 13 * Undefined（未定義）類型的值只有一個，就undefind14 * 當聲明一個變數，但是並不給變數賦值時，它的值就是undefined15 * 使用typeof檢查一個undefined時也會返回undefined16 */17 var a = null;18 console.log(typeof a); //object19 20 var b = undefined;21 console.log(typeof b); //undefined22 23 </script>24 </head>25 <body>26 </body>27 </html>
JS基礎_Null和Undefined
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