JavaScript中用千分位格式化数字

function formatThousand(num) {
    num = num + "";
    var reg = /(-?\d+)(\d{3})/;
    while (reg.test(num)) {
        var temp = num.replace(reg, "$1,$2");
        if (num.indexOf(".") >= 0 && temp.split(".")[1].length > num.split(".")[1].length) {
            break;
        }
        num = temp;
    }
    return num;
}