基础包装类型

var s1 ="some text"
s1.color="red";
alert(s1.color);   //undefined

var value="25";
var number =Number(value);  //转为函数
alert(typeof number  )    //number

var obj =new Number(value);
alert(typeof obj)   //object


var falseObject =new Boolean(false);
var result falseObject && true;
alert(result)   //true

var falseValue =false;
result =falseValue && true;
alert(result);   //false;

//toString()方法传递一个表达基数的参数，告诉它返回几进制数值的字符串，
var num =10;
alert(num.toString());//10
alert(num.toString(2));//1010
alert(num.toString(8));//12
alert(num.toString(10));//10
alert(num.toString(16));//a

toFixd()方法会按照指定的小数位返回数值的字符串表示
var num =10;
alert(num.toFixed(2));  //"10.00"

var num1 = 10.005;
alert(num1.toFixed(2));

var stringValue ="hello world";
alert(stringValue.slice(3))  //lo world
alert(stringValue.substring(3))  //lo world
alert(stringValue.substr(3)) //lo world
alert(stringValue.slice(3,7))   //lo w
alert(stringValue.substring(3,7)) //lo w
alert(stringValue.substr(3,7))    //lo worl
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var stringValue ="hello world";
alert(stringValue.slice(-3))  //rld
alert(stringValue.substring(-3))  //hello world
alert(stringValue.substr(-3)) //rld
alert(stringValue.slice(3,-4))   //lo w
alert(stringValue.substring(3,-4)) //hel
alert(stringValue.substr(3,-4))    //""

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var stringValue ="hello world";
alert(stringValue.toLocaleUpperCase()); //HELLO WOERL
alert(stringValue.toUpperCase())   //HELLO WOERL
alert(stringValue.toLocaleLowerCase())  //hello world
alert(stringValue.toLowerCase())   //hello world