Default Arguments for Functions

// Combiner of passed arguments and defaults (usable with any function)
Object.prototype.combine = function(_args){
  for(var i in this) {
    if(typeof _args[i] == "undefined") {
      _args[i] = this[i];

// Specific example function with defaults
function feedTheCat(args){
  var defaults = {
      'morning' : "nothing",
      'noon'    : "pork",
      'nite'    : "mouse"

// USAGE: only passing 2 of 3 arguments
  'morning': "milk", 
  'nite': "kitekat"

// Values would be: milk | pork | kitekat


  1. User Avatar

    Thanks, perfect solution.

  2. User Avatar
    Permalink to comment#

    or $.extend in jQuery

  3. User Avatar
    Reza Baiat
    Permalink to comment#

    FIX BUG!

    <script type="text/javascript">
    Object.prototype.combine = function(_args){
       for(var i in this) {
          if(typeof _args[i] == "undefined") {
                   this[i] = _args[i];    // BugFix: assignment parts are swapped
  4. User Avatar
    Permalink to comment#

    Is preferably to not use an prototype for Object, you will have issues when will try to foreach it, this prototype will appear in the list of all objects and you will have to use hasOwnProperty to omit it, so better use simple functions.

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