var str = new String();
 var str = new String('hello world');//初始化str,str.length = 11;

var strValue = new String('hello world');
console.log(strValue.charAt(1));//e
console.log(strValue[1]);//e,IE7及以下版本使用这种方式，会返回undefined

var strValue = new String('hello world');
console.log(strValue.charCodeAt(1));//101

var str = 'hello world'
str.indexOf('l');//2,返回找到的第一个字符的位置
str.indexOf('l',6);//9

var str = new String('hello');
var result = str.concat(' world');
console.log(result);//hello world
typeof result//"string"

var str = 'hello';
str.slice(0,2);//"he",第一个参数指定字符串开始的位置，第二个参数表示字符串到哪里结束
str.slice(-3);//"llo",o代表-1，依次倒数，-3代表倒数第三个的l
str.slice(-2,-1);//"l",同理，-2代表倒数第二个l,-1代表倒数第一的o

var str = 'hello';
str.substring(0,2);//"he",此时的参数意义同str.slice(0,2)
str.substring(-3);//"hello",substring()方法会把所有负值参数转换为0
str.substring(-3,-2);//"",同上

var str = 'hello';
str.substr(1,2);//"el",第一个参数指定字符串的开始位置，第二个参数指定的则是返回的字符个数
str.substr(-3);//"llo",此时的参数意义同str.slice(-3)
str.substr(-3,-1);//"",substr()方法会将负的第二个参数转换为0

var color = 'blue,red,orange';
color.split();//["red,blue,orange"],长度为1
color.split(',');//["blue", "red", "orange"],长度为3
var color = 'blue-red-orange';
color.split('-');//["blue", "red", "orange"]，长度为3
color.split(',',2);//["blue", "red"]

var str = 'hello';
str.toUpperCase();//"HELLO"
str.toLowerCase();//"hello"

var str = ' hello world ';
str.trim()//"hello world"

var text = 'cat, bat, sat, fat';
var pattern = /.at/;

var matches = text.match(pattern);
matches // ["cat"]
matches.input // "cat, bat, sat, fat"
matches.index // 0

var text = 'cat, bat, sat, fat';
var pattern = /at/;

text.search(pattern) // 1

var text = 'xxx-love-xxx';
var pattern = /xxx/g;

var result = text.replace(pattern,'2')
result// "2-love-2"

text.replace(/(xxx)-\w{4}-(xxx)/g,'I love YOU');//"I love YOU"
var text = 'xxx-love-xxx';
var pattern1 = /xxx/g;

var result = text.replace(pattern1,'$$')
result// "$-love-$"

var result = text.replace(pattern1,'$&2')
result//"xxx2-love-xxx2"

var result = text.replace(pattern1,'$\'')
result//"-love-xxx-love-"