<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>Title</title>
</head>
<body>
<script type="text/javascript">
var str='123asd';
//法1
console.log(typeof str==='string'); //true
//法2
console.log(str.constructor===String); //true
console.log(str instanceof String); //false
//法3
console.log(Object.prototype.toString.call(str)==='[object String]')
</script>
</body>
</html>
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