String.repeat()

/**
 * String.prototype.repeat() polyfill
 https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/repeat#Polyfill
 */
if (!String.prototype.repeat) {
	String.prototype.repeat = function(count) {
		'use strict';
		if (this == null)
			throw new TypeError('can\'t convert ' + this + ' to object');

		var str = '' + this;
		// To convert string to integer.
		count = +count;
		// Check NaN
		if (count != count)
			count = 0;

		if (count < 0)
			throw new RangeError('repeat count must be non-negative');

		if (count == Infinity)
			throw new RangeError('repeat count must be less than infinity');

		count = Math.floor(count);
		if (str.length == 0 || count == 0)
			return '';

		// Ensuring count is a 31-bit integer allows us to heavily optimize the
		// main part. But anyway, most current (August 2014) browsers can't handle
		// strings 1 << 28 chars or longer, so:
		if (str.length * count >= 1 << 28)
			throw new RangeError('repeat count must not overflow maximum string size');

		var maxCount = str.length * count;
		count = Math.floor(Math.log(count) / Math.log(2));
		while (count) {
			 str += str;
			 count--;
		}
		str += str.substring(0, maxCount - str.length);
		return str;
	}
}