var stringValue = "hello world";
alert(stringValue.charAt(1)); //"e"
//如果你想得到是不是字符而是字符编码
var stringValue = "hello world";
alert(stringValue.charCodeAt(1)); //输出"101"

var stringValue = "hello ";
var resrult = stringValue.concat("world");
alert(resrult); //"hello world"
alert(stringValue); //"hello "

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"
//返回7个字符
alert(stringValue.substring(3,7)); //"lo worl"

var stringValue = "hello world";
alert(stringValue.indexOf("o"));  //4
alert(stringValue.lastIndexOf("o")); //7

var stringValue = " hello world ";
var trimSting = stringValue.trim();
alert(trimSting); //"hello world"
alert(stringValue); //" hello world "

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

var text = "cat,bat,sat,fat";
var pos = text.search(/at/);
alert(pos); //1

var text = "cat,bat,sat,fat";
var result = text.replace("at","ond");
alert(result); //"cond,bat,sat,fat"
result = text.replace(/at/g,"ond");
alert(result); //"cond,bond,sond,fond"