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

var myObject = {
    "ircEvent": "PRIVMSG",
    "method": "newURI"
};

delete myObject.regex;
// or,
delete myObject['regex'];
// or,
var prop = "regex";
delete myObject[prop];

function contains(a, obj) {
    for (var i = 0; i < a.length; i++) {
        if (a[i] === obj) {
            return true;
        }
    }
    return false;
}

• Dojo Toolkit: dojo.indexOf(array, value, [fromIndex, findLast])
• Prototype: array.indexOf(value)
• MooTools: array.indexOf(value)
• MochiKit: findValue(array, value)
• MS Ajax: array.indexOf(value)
• Ext: Ext.Array.contains(array, value)
• Lodash: _.includes(array, value, [from]) (is _.contains prior 4.0.0)

Languages that compile to JavaScript

a = [1, 2, 3, 4]
alert(2 in a)

var mylist = [1, 2, 3];
assert(mylist.contains(1));
assert(mylist.indexOf(1) == 0);

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

var myObject = {
    "ircEvent": "PRIVMSG",
    "method": "newURI"
};

delete myObject.regex;
// or,
delete myObject['regex'];
// or,
var prop = "regex";
delete myObject[prop];

Answer : 

      Note: This is a reply to another answer, not a proper response to this question. If you wish to       have fast object cloning please follow Corban's advice in their answer to this question.

// Shallow copy
var newObject = jQuery.extend({}, oldObject);

// Deep copy
var newObject = jQuery.extend(true, {}, oldObject);

var myObject = new Object();
myObject["firstname"] = "Gareth";
myObject["lastname"] = "Simpson";
myObject["age"] = 21;

Answer : 

Object.size = function(obj) {
    var size = 0, key;
    for (key in obj) {
        if (obj.hasOwnProperty(key)) size++;
    }
    return size;
};

// Get the size of an object
var size = Object.size(myArray);

var size = Object.keys(myObj).length;