SOURCE

        var $a=10;
        var a=3.14;
        var string = "I am a string";
        var notDefined;
        var noSpace = null;
        var isReal=true;

        document.write($a+"<br/>");
        document.write(a+"<br/>");
        document.write(string+"<br/>");
        document.write(notDefined+"<br/>");
        document.write(noSpace+"<br/>");

        document.write("--------------------------------<br/>");

        var number1=10;
        var number2=20;
        var sum=number1+number2;
        var string1="Hi";
        var string2="Hello";
        var string1Number1=string1+number1;
        var number2String2=number2+string2;
        var string1Number1=number1+"";
        var string1Number1Number2=string1Number1+number2;

        document.write(sum+"<br/>");
        document.write(string1Number1+"<br/>");
        document.write(number2String2+"<br/>");
        document.write(string1Number1Number2+"<br/>");
        document.write(string1+string2+"<br/>");

        document.write("--------------------------------<br/>");
        //赋值运算符
        var a=1;
        var b=2;

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

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

        document.write("--------------------------------<br/>");
        //比较运算符
        var larger=(1+2)>(2+3);
        document.write("(1+2) > (2+3) :" + larger + "<br/>");

        var smaller=(1+2)<(2+3);
        document.write("(1+2) < (2+3) :" + smaller + "<br/>");

        var largeEqual=(1+2) <= (2+3);
        document.write("(1+2) <= (2+3) :" + largeEqual + "<br/>");

        var equal = ((2+2) == 4);
        document.write("((2+2) == 4) :" + equal + "<br/>");

        var notEqual=((2+2) != 4);
        document.write("((2+2) != 4) :" + notEqual + "<br/>");

        document.write("--------------------------------<br/>");
        //逻辑运算符

        var intersection = true && (1>2);
        document.write("true && (1>2) :" + intersection + "<br/>");

        var union = true || (1>2);
        document.write("true || (1>2) :" + union + "<br/>");

        var not = !(1>2);
        document.write("!(1>2) :" + not + "<br/>");

        document.write("--------------------------------<br/>");
        //条件运算符
        var condition = (5<7)? "是": "否";
        document.write('(5<7)? "是": "否"' + condition + "<br/>");

        document.write("--------------------------------<br/>");
        //字符串转数字
        var a = Number("2018") + 1000;
        document.write(a + "<br/>");

        document.write("Number('123')：" + Number("123") + "<br/>");
        document.write("Number('3.1415')：" + Number("3.1415") + "<br/>");
        document.write("Number('hao123')：" + Number("hao123") + "<br/>");
        document.write("Number('100px')：" + Number("100px"));

        document.write("parseInt('123')：" + parseInt("123") + "<br/>");
        document.write("parseInt('3.1415')：" + parseInt("3.1415") + "<br/>");
        document.write("parseInt('hao123')：" + parseInt("hao123") + "<br/>");
        document.write("parseInt('100px')：" + parseInt("100px")+ "<br/>");
        document.write("parseInt('+123')：" + parseInt("+123") + "<br/>");
        document.write("parseInt('-123')：" + parseInt("-123")+ "<br/>");

        document.write("parseFloat('123')：" + parseFloat("123") + "<br/>");
        document.write("parseFloat('3.1415')：" + parseFloat("3.1415") + "<br/>");
        document.write("parseFloat('hao123')：" + parseFloat("hao123") + "<br/>");
        document.write("parseFloat('100px')：" + parseFloat("100px") + "<br/>");

        document.write("--------------------------------<br/>");
        // 数字转字符串
        var a = 2018 + "";
        var b = a + 1000;
        document.write(b + "<br/>");

        var a = 2000;
        var b = a.toString() + 1128;
        document.write(b + "<br/>");

        document.write("--------------------------------<br/>");
        //转义字符
        document.write("绿叶，给你\"初恋\"般的感觉~");

<!DOCTYPE html> 
<html>
<head>
    <meta charset="utf-8" />
    <title></title>
    
</head>
<body>
    <script>
        var $a=10;
        var a=3.14;
        var string = "I am a string";
        var notDefined;
        var noSpace = null;

        document.write($a+"<br/>");
        document.write(a+"<br/>");
        document.write(string+"<br/>");
        document.write(notDefined+"<br/>");
        document.write(noSpace+"<br/>");
        document.write("--------------------------------<br/>");
        var number1=10;
        var number2=20;
        var sum=number1+number2;
        var string1="Hi";
        var string2="Heather";
        var string1Number1=string1+number1;
        var number2String2=number2+string2;
        var string1Number1=number1+"";
        var string1Number1Number2=string1Number1+number2;
        document.write(sum+"<br/>");
        document.write(string1Number1+"<br/>");
        document.write(number2String2+"<br/>");
        document.write(string1Number1Number2+"<br/>");
        document.write(string1+string2+"<br/>");
        document.write("--------------------------------<br/>");
        

    </script>
</body>
</html>