check the change of lastIndex,and in greedy match what the result like.<http://jsfiddle.net/earlybird/RrZKH/2/>

正则表达式lastIndex

//1.with greedy match and global flag
var re = /\s*/g;
for (var i = 0; i < 6; i++) {
    console.log(re.exec('    as  '));
    console.log(re.lastIndex);//4,4,4,4,4,4
}

//2.without greedy match ,but global flag
var re1 = /\s/g;
for (var i = 0; i < 6; i++) {
    console.log(re1.exec('    as  '));
    console.log(re1.lastIndex);//1,2,3,4,7,8
}

//3.match failed, without greedy match ,but global flag
var re2 = /\s*/g;
for (var i = 0; i < 6; i++) {
    console.log(re2.exec('as'));//''(empty string),...
    console.log(re2.lastIndex);//0,0,0,0,0,0
}

//4.match failed, without greedy match ,but global flag
var re3 = /\s/g;
for (var i = 0; i < 6; i++) {
    console.log(re3.exec('as'));// null ...
    console.log(re3.lastIndex);//0,0,0,0,0,0
}​

/***********************************************************************/
var re = /hi?/g; 
for(var i = 0;i<10;i++){
re .exec('hi');
console.log(re.lastIndex); // 2,0,2,0,2,0,2,0,2,0
}

var re = /(hi)?/g; 
for(var i = 0;i<10;i++){
re .exec('hi');
console.log(re.lastIndex);//2,2,2,2,2,2,2,2,2,2
}


the diff between non-parentheses and parentheses.

http://www.cnblogs.com/_franky/archive/2010/05/02/1725859.html