String.prototype.padStart = String.prototype.padStart ? String.prototype.padStart : function(targetLength, padString) {
    targetLength = Math.floor(targetLength) || 0;
    if(targetLength < this.length) return String(this);

    padString = padString ? String(padString) : " ";

    var pad = "";
    var len = targetLength - this.length;
    var i = 0;
    while(pad.length < len) {
        if(!padString[i]) {
            i = 0;
        }
        pad += padString[i];
        i++;
    }

    return pad + String(this).slice(0);
};

if (typeof module !== 'undefined' && module.exports) {
    module.exports = String.prototype.padStart;
}