var expression = /pattern/flags;
//var expression = new RegExp("pattern","flags");
//pattern：正则表达式串
//flags有3种可混合选择：
//1、g：全局模式，该模式应用与所有字符串，而非在发现第一个匹配项就停止
//2、i：不区分大小写
//3、m：多行模式，在达到一行文本末尾时还会继续查找下一行文本 

var text = "mom and dad and baby";var pattern = /mom( and dad( and baby)?)?/gi;
var matches = pattern.exec(text);alert(matches.index);    //0
alert(matches.input);    //"mom and dad and baby"
alert(matches[0]);       //"mom and dad and baby"
alert(matches[1]);       //" and dad and baby"
alert(matches[2]);       //" and baby"

        var text = "cat, bat, sat, fat";        var pattern1 = /.at/;var matches = pattern1.exec(text);        alert(matches.index);    //0alert(matches[0]);       //"cat"alert(pattern1.lastIndex);//0
matches = pattern1.exec(text);        alert(matches.index);    //0alert(matches[0]);       //"cat"alert(pattern1.lastIndex);//0var pattern2 = /.at/g;var matches = pattern2.exec(text);        alert(matches.index);    //0alert(matches[0]);       //"cat"alert(pattern2.lastIndex);//0
matches = pattern2.exec(text);        alert(matches.index);    //5alert(matches[0]);       //"bat"alert(pattern2.lastIndex);//0

var text = "cat, bat, sat, fat";
var pattern = /.at/;if (pattern.test(text)){alert("The pattern was matched.");
}

var r, re;         // 声明变量。
var s = "The rain in Spain falls mainly in the plain";
re = /ain/ig;      // 创建正则表达式模式。
r = s.match(re);   // 尝试去匹配搜索字符串，没匹配则返回null
return(r);         // 返回的数组包含了所有 "ain" 出现的四个匹配。如果没加全局标识则返回第一个"ain"

var text = "this has been a short summer";
var pattern = /(.)hort/g;/** Note: Opera doesn't support input, lastMatch, lastParen, or multiline.* Internet Explorer doesn't support multiline.
*/
if (pattern.test(text)){
alert(RegExp.input);               //this has been a short summer  输入值
//alert(RegExp.$_); 

alert(RegExp.leftContext);         //this has been a      匹配项的左边的内容
//alert(RegExp["$·"]); 

alert(RegExp.rightContext);        // summer   匹配项右边的内容
//alert(RegExp["$'"]); 

alert(RegExp.lastMatch);           //short 最近一次匹配的匹配项
//alert(RegExp["$&"]); 

alert(RegExp.lastParen);           //s  最近一次匹配的捕获组
//alert(RegExp["$+"]); 

alert(RegExp.multiline);           //false  是否使用了多行模式//alert(RegExp["$*"]);
}