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var number1 = 22;
var number2 = 33;
var myString = 'Heather';

var sum = number1 + number2;
document.write(sum + '<br/>');
//数字相加等于数字
var sumString = number1 + myString;
document.write(sumString + '<br/>');
//字符串相加等于相连接
var stringSum = myString + number2;
document.write(stringSum + '<br/>');

var stringNum = number1 + "";

var stringNumSum = stringSum + number2;
document.write(stringSum + '<br/>');

document.write('---------------<br/>');
//3.1 王婷婷 20054036 
//赋值运算符
var left = 1 ;
var right = 2 ;

left += right ;
document.write(left+'<br/>');

left -=right;
document.write(left+'<br/>');

left *=right;
document.write(left+'<br/>');

left /=right;
document.write(left+'<br/>');

document.write('---------------<br/>');
//比较运算符
left = (1+2) + 3; //等于5
right = (3+4) + 1; //等于8

document.write( (left>right) + '<br/>' );
document.write( (left<right) + '<br/>' );
document.write( (left>=right) + '<br/>' );
document.write( (left<=right) + '<br/>' );

document.write('---------------<br/>');
//逻辑运算符
var logicOperation = false;

logicOperation = (left > right) && (left <right);
document.write(logicOperation + '<br/>');

logicOperation = true && (left <right);
document.write(logicOperation + '<br/>');

logicOperation = (left > right) || (left <right);
document.write(logicOperation + '<br/>');

logicOperation = (left > right) || false ;
document.write(logicOperation + '<br/>');

logicOperation = !(left > right);
document.write(logicOperation + '<br/>');
logicOperation = !(left <right);
document.write(logicOperation + '<br/>');

document.write('---------------<br/>');
//字符串和数字的互相转换
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")+'<br/>');

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

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

document.write('---------------<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/>');
var result = (2<1)? "小芳" : "小美";
document.write(result);

document.write('<br/>---------------<br/>');
var number = 1;

//把数字转换成字符串
var stringNumber = 1 + "" ;
var stringNumber2 = number.toString() ;

document.write(stringNumber + '<br/>');
document.write(stringNumber2 + '<br/>');

<!DOCTYPE html> 
<html>
<head>
    <meta charset="utf-8" />
    <title></title>
    <script>
        var $a = 3;
        //var a;
        //var myString = 'Heather';
        //var noSpace = null;
        //var isReal = true;

        document.write($a + '<br/>');
        //document.write(myString + '<br/>');
        //document.write(noSpace + '<br/>');
        //document.write(isReal + '<br/>');
       
    </script>
</head>
<body>
</body>
</html>