Here you can find the source of format()
String.prototype.format = function() { var newStr = this, i = 0; while (/%s/.test(newStr)) newStr = newStr.replace("%s", arguments[i++]) return newStr; }
String.prototype.format = function() { var args = arguments; return this.replace(/\{(\d+)\}/g, function (m, n) { return args[n]; }); };
String.prototype.format=function(){ var a=arguments; return this.replace(/\{(\d+)\}/g,function(b,c){return a[c]}) };
String.prototype.format = function() { a = this; for (k in arguments) { a = a.replace("{" + k + "}", arguments[k]); return a; };
String.prototype.format = function() { var args = arguments; return this.replace(/{(\d{1})}/g, function() { return new String(args[arguments[1]]); }); };
String.prototype.format=function(){ if(0==arguments.length) return this; var t=arguments; return this.replace(/\{(\d+)\}/g,function(r,n){ return void 0===t[n]?"{"+n+"}":t[n]}) };
String.prototype.format = function() { var args = arguments; return this.replace(/\{(\d+)\}/g, function() { return args[arguments[1]]; }); };
String.prototype.format = function() var args = arguments; return this.replace(/\{(\d+)\}/g, function(m,i){ return args[i]; });
String.prototype.format = function(){ var args = arguments; return this.replace(/\{(\d)\}/g, function(a,b){ return typeof args[b] != 'undefined' ? args[b] : a; });
var util = require('util'); String.prototype.format = function () { return util.format.apply(null, [ this.toString() ].concat(Array.prototype.slice.call(arguments))); };