How to list the properties of a JavaScript object?

Say I create an object thus:

var myObject =
        {"ircEvent": "PRIVMSG", "method": "newURI", "regex": "^http://.*"};

What is the best way to retrieve a list of the property names? i.e. I would like to end up with some variable ‘keys’ such that:

keys == ["ircEvent", "method", "regex"]

Answer

In modern browsers (IE9+, FF4+, Chrome5+, Opera12+, Safari5+) you can use the built in Object.keys method:

var keys = Object.keys(myObject);

The above has a full polyfill but a simplified version is:

var getKeys = function(obj){
   var keys = [];
   for(var key in obj){
      keys.push(key);
   }
   return keys;
}

Alternatively replace var getKeys with Object.prototype.keys to allow you to call .keys() on any object. Extending the prototype has some side effects and I wouldn’t recommend doing it.