javascript string padding function

javascript string object doesn’t come with string padding function. Here is a a string padding function that takes three parameters, string, width and padding. It converts the string to a string of the specified width and padding.

function strPad(str, width, padding) {
	if (typeof str === 'string' || typeof str === 'number') {
		str = str + '';
	} else {
		throw 'str has to be type string or number.';
	}

	if (typeof width !== 'number') {
		throw 'width has to be a number.'; 
	}

	if (typeof padding !== 'string') {
		throw 'padding has to be a string.';
	}

	if (padding.length === 0) {
		throw 'padding cannot be an empty string.';
	}

	while (str.length < width) {
		str = padding + str;
	}
	return str;
}

Examples:

var strings = ['1222',123,""];
for(var i=0; i<strings.length; i++) {
	console.log(strPad(strings[i],10,'0'));
}
console.log(strPad("111",10,'0'));
console.log(strPad("222",-2,' '));
console.log(strPad("333",0,' '));

// outputs:
// 0000001222
// 0000000123
// 0000000000
// 0000000111
// 222
// 333