function pad( str, len, options ) {
	var nright;
	var nleft;
	var isodd;
	var right;
	var left;
	var opts;
	var err;
	var tmp;
	var n;
	if ( !isString( str ) ) {
		throw new TypeError( format( 'invalid argument. First argument must be a string. Value: `%s`.', str ) );
	}
	if ( !isNonNegativeInteger( len ) ) {
		throw new TypeError( format( 'invalid argument. Second argument must be a nonnegative integer. Value: `%s`.', len ) );
	}
	if ( len > FLOAT64_MAX_SAFE_INTEGER ) {
		throw new RangeError( format( 'invalid argument. Output string length exceeds maximum allowed string length. Value: `%u`.', len ) );
	}
	opts = {};
	if ( arguments.length > 2 ) {
		err = validate( opts, options );
		if ( err ) {
			throw err;
		}
	}
	if ( opts.lpad && opts.rpad ) {
		n = ( len-str.length ) / 2;
		if ( n === 0 ) {
			return str;
		}
		tmp = floor( n );
		if ( tmp !== n ) {
			isodd = true;
		}
		if ( n < 0 ) {
			n = floor( abs( n ) );
			nleft = n;
			nright = str.length - n;

			// If |len-str.length| is an odd number, take away an additional character from one side...
			if ( isodd ) {
				if ( opts.centerRight ) {
					nright -= 1;
				} else {
					nleft += 1;
				}
			}
			return str.substring( nleft, nright );
		}
		nleft = ceil( n / opts.lpad.length );
		left = repeat( opts.lpad, nleft );

		nright = ceil( n / opts.rpad.length );
		right = repeat( opts.rpad, nright );

		// If (len-str.length) is an odd number, give one side one extra character...
		n = tmp;
		nleft = n;
		nright = n;
		if ( isodd ) {
			if ( opts.centerRight ) {
				nleft += 1;
			} else {
				nright += 1;
			}
		}
		left = left.substring( 0, nleft );
		right = right.substring( 0, nright );
		return left + str + right;
	}
	if ( opts.lpad ) {
		tmp = lpad( str, len, opts.lpad );
		return tmp.substring( tmp.length-len );
	}
	if ( opts.rpad ) {
		return ( rpad( str, len, opts.rpad ) ).substring( 0, len );
	}
	if ( opts.rpad === void 0 ) {
		return ( rpad( str, len, ' ' ) ).substring( 0, len );
	}
	throw new RangeError( format( 'invalid argument. At least one padding option must have a length greater than 0. Left padding: `%s`. Right padding: `%s`.', opts.lpad, opts.rpad ) );
}
Pads a string such that the padded string has a length of `len`.

@param {string} str - string to pad
@param {NonNegativeInteger} len - string length
@param {Options} [options] - function options
@param {string} [options.lpad=''] - string used to left pad
@param {string} [options.rpad=' '] - string used to right pad
@param {boolean} [options.centerRight=false] - boolean indicating whether to center right in the event of a tie
@throws {TypeError} first argument must be a string
@throws {TypeError} second argument must be a nonnegative integer
@throws {TypeError} options argument must be an object
@throws {TypeError} must provide valid options
@throws {RangeError} at least one padding must have a length greater than `0`
@returns {string} padded string

@example
var str = pad( 'a', 5 );
// returns 'a    '

@example
var str = pad( 'a', 10, {
    'lpad': 'b'
});
// returns 'bbbbbbbbba'

@example
var str = pad( 'a', 12, {
    'rpad': 'b'
});
// returns 'abbbbbbbbbbb'

@example
var opts = {
    'lpad': 'a',
    'rpad': 'c'
};
var str = pad( 'b', 10, opts );
// returns 'aaaabccccc'

@example
var opts = {
    'lpad': 'a',
    'rpad': 'c',
    'centerRight': true
};
var str = pad( 'b', 10, opts );
// returns 'aaaaabcccc'