substring从右边获取指定长度字符串

转自：http://dev.mjxy.cn/a-substring-from-the-right-to-obtain-the-specified-length-of-string.aspx

/*
   Get the rightmost substring, of the specified length,
   from a String object.
*/

String.prototype.right = function (length_)
{
        var _from = this.length - length_;
        if (_from < 0) _from = 0;
        return this.substring(this.length - length_, this.length);
};