javascript当中类型转换，typeof的用法_typeof number == typeof window-优快云博客

本文链接：https://blog.youkuaiyun.com/mark_to_win/article/details/88602799

博客主要介绍了JavaScript中类型转换及typeof的用法。通过示例展示了使用Number()、String()等方法进行类型转换，如将数字转换为字符串，将字符串转换为数字等，并使用typeof输出变量类型。还提及部分代码在不同环境的执行情况。

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1）类型转换，typeof的用法

例 3.1.1

<HTML>
<head>
    <meta http-equiv="content-type" content="text/html; charset=utf-8"/>
</head>
<BODY>
<SCRIPT LANGUAGE="JavaScript">
    <!--
    /*
    Cast operator (Definition) refer to 过去的网站www.favo.com
    A way of converting data types.
    Primitive values can be converted from one to another or rendered as objects by using object constructors to convert the values.

    Boolean
    Number
    String

    Number() (Function) 马克-to-win: actually Number() is the method of Global object.
    A Number type convertor.

    Property/method value type: Number primitive
    JavaScript syntax: - Number()
    - Number(aValue)
    Argument list: aValue A value to be converted to a number.

    When the Number() constructor is called as a function, it will perform a type conversion.
    The following values are yielded as a result of calling Number() as a function:

    Value                            Result
    Number                            No conversion, the input value is returned unchanged.
    Non numeric string                NaN

    window.Number("23");在favo中查不出来，但Idea中可以打点打出来。
    */
    var a = 9;
/*下句话如果放在ie8中执行，必须打开debug工具*/
//    console.log(typeof(a));
    document.writeln(typeof(a));
    var as = String(a);
    //String是Global的方法
    document.writeln("typeof(as) is " + typeof(as));
    var x = window.Number("23");
    document.writeln("typeof(x) is " + typeof(x));
    var age2 = Number("56");
    document.writeln(typeof(age2) + "is typeof(age2)");
    var age3 = new Number(56);