Left pad of string/number

pad.js

/**
 * Pads from left given subject with specified character.
 * @param {string|number} number number or string to pad
 * @param {number} width width of a subject
 * @param {string|number} char character to pad
 * @returns {string} padded subject
 */
function pad( number, width, char )
{
	char = char || '0';
	number = number + '';
	return number.length >= width ? number : new Array( width - number.length + 1 ).join( char ) + number;
}

var d = new Date(),
	file_name = 'backup_' 
	+ d.getFullYear() 
	+ pad( d.getMonth() + 1, 2 ) 
	+ pad( d.getDate(), 2 ) 
	+ pad( d.getHours(), 2 ) 
	+ pad( d.getMinutes(), 2 ) 
	+ pad( d.getSeconds(), 2 ) + '.tar.gz';

console.log('File name:', file_name); // File name: backup_20140130160905.tar.gz