Javascript strPad function

str_pad.js

function str_pad(input, pad_length, pad_string, pad_type){
	var output = input.toString();
	if (pad_string === undefined) { pad_string = ' '; }
	if (pad_type === undefined) { pad_type = 'STR_PAD_RIGHT'; }
	if (pad_type == 'STR_PAD_RIGHT') {
		while (output.length < pad_length) {
			output = output + pad_string;
		}
	} else if (pad_type == 'STR_PAD_LEFT') {
		while (output.length < pad_length) {
			output = pad_string + output;
		}
	} else if (pad_type == 'STR_PAD_BOTH') {
		var j = 0;
		while (output.length < pad_length) {
			if (j % 2) {
				output = output + pad_string;
			} else {
				output = pad_string + output;
			}
			j++;
		}
	}
	return output;
};