lovecoding
/
W260426


			
				
					
						
						
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							<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <!-- 判断数据类型 -->
     <script>
        // 判断数据类型
        let str = "hello";
        let num = 100;
        let bool = true;
        let nul = null;
        let unde = undefined;
        let obj = {a:1};
        let arr = [1,2,3];

        // 方法一：typeof 他不能判断 null、Array、Object
        // console.log(typeof str);
        // console.log(typeof num);
        // console.log(typeof bool);
        // console.log(typeof nul);
        // console.log(typeof unde);
        // console.log(typeof obj);
        // console.log(typeof arr);

        // 方法二：instanceof 
        // console.log(str instanceof String);
        // console.log(num instanceof Number);
        // console.log(bool instanceof Boolean);
        // // 注意：null、undefined 不能用 instanceof 判断
        // // console.log(nul instanceof null);
        // // console.log(unde instanceof undefined);
        // console.log(obj instanceof Object);
        // console.log(arr instanceof Array);

        // 方法三：Object.prototype.toString.call() 可以判断任何类型
        // console.log(obj.toString());
        // console.log(Object.prototype.toString.call(str));
        // console.log(Object.prototype.toString.call(num));
        // console.log(Object.prototype.toString.call(bool));
        // console.log(Object.prototype.toString.call(nul));
        // console.log(Object.prototype.toString.call(unde));
        // console.log(Object.prototype.toString.call(obj));
        // console.log(Object.prototype.toString.call(arr));

        // 方法四：Array.isArray() 只能判断 Array 类型
        // console.log(Array.isArray(arr));
        // console.log(Array.isArray(obj));
     </script>
</body>
</html>