js中扩展padLeft、padRight

    //方法一
    function FillZero(p) {
        return new Array(3 - (p + '').length + 1).join('0') + p;
    }
    FillZero(6);    //输出006

    //方法一扩展（C#中PadLeft、PadRight）
    String.prototype.PadLeft = function (len, charStr) {
        var s = this + '';
        return new Array(len - s.length + 1).join(charStr || '') + s;
    }
    String.prototype.PadRight = function (len, charStr) {
        var s = this + '';
        return s + new Array(len - s.length + 1).join(charStr || '');
    }
    var p = 6;
    p.toString().PadLeft(3, '0');    //输出006
    p.toString().PadRight(3, '0');  //输出600