js，千分符

function formatNum(num) {
    num=(num+'').match(/^(?:\s*)(\-?\d+)(\.(\d+))?(?:\s*)$/);
    if(!num)return '';
    var int=num[1].split('');
    for(var i=int.length;i>0;i-=3)
        (i!==int.length)&&int.splice(i,0,',');
    num[2]&&int.push(num[2]);
    return int.join("");
}

formatNum(123124.1252564353)				//"123,124.1252564353"
formatNum(123124)					//"123,124"
formatNum('123225676245342341676435134.23')		//"123,225,676,245,342,341,676,435,134.23"
formatNum(-23412412)					//"-23,412,412"