format.js

String.prototype.format = String.prototype.f = function(arg){
	var is_object = typeof arg === 'object',
		keys = is_object ? Object.keys(arg) : (function(l){for(i=0,a=[];i<l;i++)a[i]=i;return a;})(arguments.length),
		args = is_object ? arg : arguments;

	return this.replace( new RegExp('\\{(keys)\\}'.replace('keys', keys.join('|')), 'gm'), function(match, key){return args[key];});
}