What are the key differences between JavaScript and ActionScript 3?

Question

I know both languages are from the same ECMA standard. It seems that the two are becoming very similar with JavaScript adding event listeners and the such. I was wondering what the differences are?

Answer 1

One is type Safetly. Actionscript requires that you set a type for all objects, and JavaScript doesn't (for that matter, in JavaScript, one variable may be one type and then immediately set to another type).

Actionscript is object oriented. Although you can sort of have this in JavaScript, Actionscript allows for object inheritance, etc.

Answer 2

I've been programming in both ActionScript and Javascript, and from a less-technical standpoint, I see two main differences.

1) JavaScript is more powerful. You are allowed to do much more with the language because it does not have a "compiler" or types. There are some great frameworks out there like ExtJS and jQuery that try and simplify things for you, but even with them, you are really allowed to do an amazing amount of damage if you want to.

2) ActionScript is much more confining and hence, much easier to maintain. Adobe did a lot of work to keep you out of the difficult parts of ECMAScript. ECMAScript Objects, prototypal inheritance, and closures are three concepts that you really don't need to understand to program in ActionScript. You just need to understand how to use Adobe's "Class" object.

For simple uses, I prefer JavaScript. However, once the project gets large, it depends who you are coding for. If I had a team of 5 developers programming at a scrappy start-up, I'd choose JavaScript in a heartbeat. However, in the girth of a large corporation, or academia, you might be safer relying on Adobe's platform.

Hope that helps.

Answer 3

Essentially the main difference I find is that ActionScript is more a verbose statically-typed class-based language where as javascript is a prototypal language.

Unfortunately there is no type-inference in ActionScript so using Flex Builder gives a warning every time you leave something untyped which I find unnecessary and overly verbose, not only does it make it more verbose than javascript but I find equivalent code to be more verbose than C#.

However the extra verbosity does have yield perf improvements and extra type safety at compile-time. Unfortunately this also adds to build time quite significantly, in Java Script apps of any size I'm used to instant feedback whereas my last ActionScript project had build time exceeding 2 minutes.

Answer 4

First of all ActionScript 3 and JavaScript are both defined in ECMA-262 so they have a lot in common. Both languages feature prototype inheritance for instance. It is however not correct that ActionScript fully implements ES4.

ActionScript implements a couple of features that are not defined in ECMA-262 and some -- but definitely not all -- of ES4.

So what does AS3 add to ECMA-262? Those are also the differences to JavaScript:

• Dynamically and statically typed code
• Packages, Classes and Interfaces
• Standard OO inheritance model (not prototype based, statically typed)
• uint and int datatype
• E4X (ECMA-357)
• Type-safe conditional compilation (ES4)
• Vector.<T> datatype (ES4)

Maybe I have forgotten some features. I am not sure if XML, XMLList etc. are already defined in 262 or came with 357.

The key difference however is the standard library. JavaScript comes with a couple of predefined classes like DOMElement and browser dependent additions. ActionScript has a fairly large standard library with features like video streaming and is consistent over all platforms.