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<!DOCTYPE html><html lang="en"><head> <meta charset="UTF-8"> <title>Typeof</title> <script> //對象不存在時返回null //變數未被賦值是undefined var test1 = "abcdef"; var test2 = 123; var test3 = true; var test4 = {}; var test5 = []; var test6; var test7 = {"abcdef": 123}; var test8 = ["abac", 123]; function test9(){return "avc"}; var test10 = null; console.log(typeof test10) //NaN是無法表示的數值,無法自身比較NaN != NaN, NaN與任何東西都不相等 //判斷NaN,任何不是數位值傳給isNaN返回的結果都是true var myNum; if (isNaN(myNum)){ myNum = 0; } alert(myNum); //Infinity指的是超過資料上限或這下限的值 if (99 == "99"){ console.log("A number equals a string"); } else { console.log("No way a number equals a strings"); } </script></head><body></body></html>
JavaScript資料類型
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