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  • JavaScript中的null和undefined

    <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
    <html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en">
    <head>
    <meta http-equiv="Content-Type" content="text/html;charset=UTF-8" />
    <title>null undefined</title>
    </head>
    <body>
    <script type="text/javascript">
            //<![CDATA[


            var a;
            var b = null;


            document.write( a + "<br/>" );  //因为a未定义具体是值,所以是undefined
            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 ); //在某些时候他们两个比较是相等的
            document.write( "<br/>" );
            document.write( 1985 === "1985" );


            //]]>
        </script>
    </body>
    </html>
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  • 原文地址:https://www.cnblogs.com/iplus/p/4490026.html
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