stringUtils.js

// http://jsperf.com/padleft/2
/**
 * String.repeat('a', 5)   = 'aaaaa'
 * String.repeat('ab', 5)  = 'ababa'
 * String.repeat('abc', 5) = 'abcab'
 */
String.repeat = function repeat(str, len) {
    while (str.length < len) {
        if (str.length * 2 >= len) {
            return str + str.substring(0, len - str.length);
        } else {
            str += str;
        }
    }

    if (str.length == len) {
        return str;
    }

    return str.substring(0, len);
};

/**
 * 'a'.padLeft('b', 5)   = 'bbbba'
 * 'a'.padLeft('ab', 5)  = 'ababa'
 * 'a'.padLeft('abc', 5) = 'abcaa'
 */
String.prototype.padLeft = function padLeft(pad, len) {
    if (this.length < len) {
        pad = pad || '  ';
        return String.repeat(pad, len - this.length) + this;
    }
    return this;
};

/**
 * 'a'.padRight('b', 5)   = 'abbbb'
 * 'a'.padRight('ab', 5)  = 'aabab'
 * 'a'.padRight('abc', 5) = 'aabca'
 */
String.prototype.padRight = function padRight(pad, len) {
    if (this.length < len) {
        pad = pad || '  ';
        return '' + this + String.repeat(pad, len - this.length);
    }
    return this;
};