Introducing JavaScript

JavaScript has changed a great deal since it was first introduced but many sites still use outdated techniques. There are even lots of JavaScript tutorials on the web that show you how JavaScript should be written so that it can work in Netscape 2 rather than so that it will work in modern browsers. As a result there are many people who are writing what they think is JavaScript but where what they are producing is more suited to the 20th Century than to the 21st.

Beginners should work through all the basic examples prior to moving on to the other examples which cover separate aspects of JavaScript in more detail.

Most of the JavaScript examples here will work in IE5+, Opera7+ and all versions of Firefox, Safari and Chrome. Those commands introduced in ECMAScript 5 in 2011 are being added to the site where they are supported by the latest version of all popular browsers. Where these new commands are not supported by IE8 or IE7 that information is included in the text since those two browsers might still have to many users for you to ignore. So few people using other browsers fail to keep their browser up to date that lack of support in older versions of other browsers will not have any significant affect.

A few examples of what we can expect from EcmaScript 6 are also included in their own section so you can see the direction that JavaScript is moving in - even though it will probably be quite a while before we can use those commands.

There is a link to jsBin at the bottom right of all the pages. This site provides an easy way to test your JavaScript code online without needing to create an entire web page to run a simple test.

Inheriting Prototype Only

JavaScript allows us to define an object that will both serve as a template for other objects and be used as an object itself. When we do this we will most likely want those objects that inherit from this object to inherit only the prototype and not the additional proerties defined on the object itself.

Prototype Chaining

Where we are using a number of “template” objects as the basis for the objects that our script is going to use we can best indicate the relationships between the objects by defining them using prototype chaining.


The instanceOf method allows us to tell if a given object was directly created from another object. The isPrototypeOf method works the other way around by and doesn’t restrict itself to direct inheritance but will instead allow for as many other intermediate objects in between as you might have created.


The hasOwnProperty method provides a way for us to tell whether references to a property of an object are referencing a property defined on the object itself or whether we are referencing the shared property attached to the prototype.

Overwriting Prototype Properties

Properties that are inherited from other objects via the prototype property are shared between all of the objects that are instances of that object. Where those objects define a property of their own with the same name they get their own separate copy of the property that they can use. If that separate property is […]

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You are welcome to use any the example JavaScript from this site in the scripts for your site or any that you develop for others but may not use the longer example scripts that contain a copyright notice in any other way without permission.