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  • 2.7.JavaScriptnull与undefined

    <!DOCTYPE HTML>
    <html lang="en-US">
    <head>
    <meta charset="UTF-8">
    <title>null和undefined</title>
    </head>
    <body>
    <script type="text/javascript">

    var a;//定义变量但没有类型所以输出为undefined
    var b = null ;//定义变量并制定值为null

    document.write( a
    + "<br/>");//
    document.write( b + "<br/>");//

    document.write( undefined
    == true );
    document.write(
    "<br/>" );
    document.write( undefined
    == "" );
    document.write(
    "<br/>" );
    document.write( undefined
    == 0 );
    document.write(
    "<br/>" );
    document.write( undefined
    == -0 );
    document.write(
    "<br/>" );
    document.write( undefined
    == NaN );
    document.write(
    "<br/>" );
    document.write( undefined
    == null);
    document.write(
    "<br/>" );
    document.write(
    1988 == "1988");
    document.write(
    "<br/>" );
    document.write(
    1988 === "1988");
    document.write(
    "<br/>" );

    </script>
    </body>
    </html>
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  • 原文地址:https://www.cnblogs.com/xiaozhanga4/p/2398086.html
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