Safe extend to bypass constructors that throw Errors.

extend.js

/**
 * This piece of code has been created to safely extend classes/objects in Javascript.
 * After talk with a great friend that was upset trying to extend a class/object that throws an error
 * if some parameter in the constructor of the class/object is missing.
 * 
 * var Search = function ( sToSearch ) {
 *    if ( sToSearch == null ) { // Check if sToSearch is null or undefined
 *        throw new Error( 'Search needs a string to search' );
 *    }
 *    this.sToSearch = sToSearch;
 *    this.sType = 'Parent';
 *    // More code
 * };
 * Search.prototype.whatToSearch = function () {
 *    alert( this.sToSearch );
 * };
 * 
 * If we try a classic prototypal inheritance we will get an error:
 * 
 * var SearchInherited = function ( sToSearch ) {
 *     Search.call( this, sToSearch );
 *     this.sType = 'Child';
 * };
 * Search.prototype = new Search();
 * Search.prototype.whatToSearch = function () {
 *     alert( 'Child what to Search: ' + this.sToSearch );
 * };
 * The solution is extend the prototype using the constructor.
 * See the code to understand it beeter.
 */

/**
 * Usage:
 * var Child = safeExtend( Parent, { property1: value, method1: function () {/* Code */} } );
 * After this you will have a Child class/object that extends from Parent.
 */

function safeExtend(oParent, oOverwiteInstanceProperties) {
	var oP, sKey;
	function F() {
		oParent.apply( this, arguments ); // Inherit the constructor members.
                
                // Set a parent reference to access to parent methods.
		this.parent = oParent.prototype;
                
                // Set the instance properties for the Child.
                // @TODO if oOverwriteInstanceProperties is a function execute it with F as context.
		for ( sKey in oOverwiteInstanceProperties ) {
			if ( oOverwiteInstanceProperties.hasOwnProperty( sKey ) ) {
				this[sKey] = oOverwiteInstanceProperties[sKey];
			}
		}
	};	
	F.prototype = new oParent.constructor();
	return F;
};