//语法

/*

var Daige = "hello";

var daige = "hello";

alert(daige);

alert(Daige);

alert(typeof(daige));

daige = 1234;

alert(typeof(daige));

//变量

var daige = "hi",age=25;

alert(typeof daige);

alert(typeof age);

test=daige;

alert(test);

//原始值和引用值

alert(typeof "hi daige");

alert(typeof null); //返回object

string = 1+"20";

alert(typeof string);

alert(typeof String); //返回function

var temp;

alert(temp);

alert(typeof temp);

alert(typeof temp1); //temp1未定义，其他运算符出错

function daige()

{

}

alert(typeof daige()); //alert(typeof daige)返回function

alert( null == undefined);

var temp;

alert( null == typeof(temp)); //false

alert( null == typeof(temp1));

alert(true);

alert(1==1);

alert(true < false);

alert(true > 0);

var t = 0x1023;

alert(t);

var f = 3.14e10;

alert(f);

alert(typeof f);

alert(isFinite(f*20000));

alert(isNaN("daige"));

var str1 = "你 好";

var str2 = "daig\"e";

var str3 = 'd';

alert(str1);

alert(str2);

alert(str3);

//转换

var num = 10;

alert(num.toString());

var isTrue = true;

alert(isTrue.toString());

var strTest = "daige";

alert(strTest.toString());

alert(num.toString(16));

alert(parseInt("123daige"));

alert(parseInt("13",16));

alert(parseInt("22.5"));

alert(parseInt("daige"));

alert(parseFloat("12.345"));

alert(Boolean("daige"));

alert(Number("23.21232"));

alert(String(123));

alert(Number("23.4.5"));

alert(parseInt("23.4.5"));

alert(String(null));

alert(String(undefined));

//引用类型

var obj = new String("daige");

alert(obj.length);

alert(obj.charAt(1));

alert(obj.concat(" hello"))

alert(obj.localeCompare());

var str1=new String("hi daige");

alert(str1.substring(2));

alert(str1.toLocaleUpperCase());

var test = new String("helo world");

alert(test instanceof String);

//运算符

var test = new String("daige");

test.name = "D";

alert(test.name);

delete test.name;

alert(test.name);

var str = "25";

str = -str;

alert(str);

alert(typeof str);

var num = 18;

alert(num.toString(2)); //10010

num = ~num; //1*27 01101

alert(num.toString());

var num = 25 & 3;

alert(num);

var num = 25 | 3;

alert(num);

var num = 25 ^ 3;

alert(num);

var num = -2;

alert(num << 5);

var comp = "Block" < "about";

alert(comp);

var comp = "Block".toLowerCase() < "about".toLowerCase();

alert(comp);

var num = "23" < "3";

alert(num);

var num = "23" < 3;

alert(num);

var str = "55";

var num = 55;

alert(str == num);

alert(str === num);

start: var num = 0;

var str = "bule";

switch(str)

{

case "blue":

break start;

case "daige":

var num = 100;

break;

default:

var num = 50;

}

alert(num);

MYLOOP: do {

x = x + 1;

if (x > 100) break MYLOOP;

continue MYLOOP;

} while (0)

alert(x);

//函数

function test(num1,num2)

{

return num1+ num2;

}

function test1(num1)

{

num3 = num1;

}

alert(test(1,2));

alert(test1(1));

function test()

{

alert(arguments[0]);

alert(arguments.length);

}

alert(test("daige","hi"));

function add()

{

if(arguments.length == 2)

{

return arguments[0]+arguments[1];

}

else if (arguments.length == 3)

{

return arguments[0]+arguments[1]+arguments[2];

}

else

return false;

}

alert(add(1,2));

alert(add(1,2,3));

var doAdd = new Function("num1","num2","alert( num1+ num2)");

function test(addFunction,num1,num2)

{

addFunction(num1,num2);

}

alert(test(doAdd,1,2));

alert(doAdd.length);

alert(doAdd.valueOf());

alert(doAdd.toString());

var totalNum = 10;

function addNum(num1,num2)

{

function doAdd() //doAdd是一个闭包 它获取外部函数参数和全局变量

{

return num1+num2+totalNum;

}

return doAdd(); //addNum调用内部函数 闭包不接受参数，它使用的的值是从执行环境获取

}

alert(addNum(1,2));

*/