Stuff You Didn't Know About ActionScript

Christophe Herreman@herrodius

... or an exploration of the ActionScript 3 language in which you might discover new things that you were not aware of and that one day might come in handy, or in which you will want to scream out WTF's so loud that the whole venue might think I'm presenting naked whilst in reality you are just looking at a piece of ActionScript code that is so counter-intuitive or looks rather puzzling you wonder how anyone came up with the idea to implement certain parts of the API this way, which on the other hand makes the language also very fun to work with once you know how to deal with these peculiarities and it becomes clear that ActionScript is actually pretty cool and powerful ...

About meRun Stack & Heap, a development, consulting and training company based in Belgium specializing in Web / RIA Development Certified expert Flex with AIR, loved Flash since 1999 Founder of Spring ActionScript and AS3Commons Apache Flex committer

Operators

Checks if 2 values are equal, and applies data conversion if the values have different data types. "hello" == "hello" // true"5" == 5 // truetrue == 1 // truefalse == 0 // true"true" == true // falsenull == undefined // true

Equality "=="

Checks if 2 values and their types are equal. "hello" === "hello" // true"5" === 5 // compile errortrue === 1 // falsefalse === 0 // false"true" === true // falsenull === undefined // false

Strict Equality "==="

Complex data types are compared by reference, not value. var a:Array = [1, 2, 3];var b:Array = [1, 2, 3];

a == b // false

var c:Array = a;

a == c // true

Equality "=="

Known as the Ternary Operator. var result:Boolean = (a > b) ? x : y; // shorthand for var result:Boolean;if (a > b) {

result = x;} else {

result = y;}

Conditional "?:"

function (a:Object) {a ||= new Object();

} // shorthand for function (a:Object) {

if (a === null) {a = new Object();

}}

Logical OR "||="

function toHTMLTag (s:String) {s &&= "<" + s + ">";return s;

} // shorthand for function toHTMLTag (s:String) {

if (s !== null && (s.length > 0))s = "<" + s + ">";

return s;}

Logical AND "&&="

Casts a value to another data type, returning null if the cast fails. "hello" as String // "hello"5 as String // nulltrue as MyClass // null String("hello") // "hello"String(5) // "5"MyClass(true) // Runtime Error

"as"

Check if a value is of a certain data type. var s:Sprite = new Sprite(); s is Sprite // trues is DisplayObject // trues is IEventDispatcher // true s instanceof Sprite // trues instanceof DisplayObject // trues instanceof IEventDispatcher // false

"is" vs "instanceof"

Identifies the namespace of an object. public namespace Dutch;public namespace French; Dutch function hello():String {

return "hallo";} French function hello():String {

return "bonjour";}

"::" name qualifier

Dutch::hello() // "hallo"French::hello() // "bonjour"

"::" name qualifier

"public", "private", "protected", "internal" are also namespaces. public function get a():String;private function set a(value:String); trace(a) // compile errora = "hello" // compile error trace(public::a)private::a = "hello"

"::" name qualifier

Check if an object contains a certain property. "CASEINSENSITIVE" in Array // true"CASEINSENSITIVE" in [] // false"length" in Array // true"length" in [] // true [].hasOwnProperty("CASEINSENSITIVE") // false[].hasOwnProperty("length") // true

"in" vs Object.hasOwnProperty

An array available in each function that contains the arguments passed to the function.

function myFunction (x:int) {for(var i:uint=0; i<arguments.length; i++){

trace(arguments[i]);}

}myFunction(1, 2, 3);// 1// 2// 3

"arguments"

Pass an arbitrary number of extra arguments to a function. function myFunction (x:int, ... rest) {

for (var i:uint = 0; i< rest.length; i++) {trace(rest[i]);

}} myFunction(1, 2, 3);// 2// 3

"..." Rest Arguments

Tips & Tricks

var a:Array = new Array();var a:Array = []; // faster var o:Object = new Object();var o:Object = {}; // faster var v:Vector.<String> = new Vector.<String>();v.push("a");v.push("b"); var v:Vector.<String> = new <String>["a", "b"];

Object creation

var a:Object = {};a.name = "John"; var b:Object = a;b.name = "Elvis"; trace(a.name); // output "Elvis"

Object References

Create deep or shallow copies depending on the scenario. // deep copy private function clone(obj:Object):Object {

var bytes:ByteArray = new ByteArray();bytes.writeObject(obj);bytes.position = 0;return bytes.readObject();

}

Object Copies

Always override the "clone" method in an Event subclass. Prevents runtime type coercion errors when redispatching. class MyEvent extends Event {

public function MyEvent(data:Object){_data = data;

}override public function clone():Event {

return new MyEvent(_data);}

}

Events

var arr:Array = ["a", "b", "c"];

// loops through keys (0, 1, 2)for ( var i in arr ) {

trace( i );}

// loop through values ("a", "b", "c")for each ( var s:String in arr ) {

trace( s );} Gotcha: order is not guaranteed, use for loop with counter

for...in vs. for each...in

You can pass multiple arguments to the trace() method. No need to compose a string. trace(new Date(2012, 4, 22), "Aloha", Math.PI, true); // Tue May 22 00:00:00 GMT+0200 2012 Aloha 3.141592653589793 true

trace()

Use "label" on a loop to name it. Useful when breaking from nested loops. mainLoop:for (var i:uint = 0; i<10; i++) {

for (var j:uint = 0; j<10; j++) {if (i == 5 && j == 7) {

break mainLoop;}

}}

Labeled Loops

Declare a single function in an *.as file and name the file the same as the function. // in file: myGlobalFunction.aspackage {

function myGlobalFunction():void {trace("in myGlobalFunction");

}}

Global Functions

Extend the behavior of built-in classes by adding methods to the prototype. Array.prototype.removeItem = function (item:*):void {

var index:int = this.indexOf(item);if (index > -1) {

this.splice(index, 1);}

}; var a:Array = [1, 2, 3];a.removeItem(2);trace(a); // 1, 3

Adding Methods to Built-in Classes

Gotchas&

WTF's

Castingvar o:MyObject = new MyObject();var o1:MyObject = MyObject(o);var o2:MyObject = o as MyObject; // o1 === o2 var a:Array = [1, 2, 3];var a1:Array = Array(a); // new Array !!!var a2:Array = a as Array; // a1 !== a2 Also the case with Date and Error classes. Watch out!

Casting to BooleanBoolean(true) // trueBoolean(false) // falseBoolean(0) // falseBoolean(1) // trueBoolean(-1) // trueBoolean("true") // trueBoolean("false") // trueBoolean("") // falseBoolean(" ") // trueBoolean("0") // trueBoolean("1") // trueBoolean(null) // falseBoolean(undefined) // falseBoolean(Object) // trueBoolean({}) // true

Array classvar a:Array = new Array(); // empty arrayvar a:Array = []; // empty array var a:Array = new Array(10); // array with length 10var a:Array = [10]; // array with 1 element: 10 var a:Array = new Array(1, 2, 3); // array with values 1, 2, 3var a:Array = [1, 2, 3]; // array with values 1, 2, 3

Date classnew Date(); // current datenew Date(2012); // 01/01/1970 01:00:02new Date(2012, 1); // 01/02/2012 00:00:00new Date(2012, 1, 1); // 01/02/2012 00:00:00 public function Date(

yearOrTimevalue:Object,month:Number, // 0 to 11date:Number = 1, // 1 to 31hour:Number = 0, // 0 to 23minute:Number = 0, // 0 to 59second:Number = 0, // 0 to 59millisecond:Number = 0) // 0 to 999

Throwing PartiesYou can throw more than just errors. class AwesomeParty {} try {

throw new AwesomeParty();} catch (party:AwesomeParty) {

// go loose at moNo!} Practical use?

More info

ActionScript 3 Language Referencehttp://help.adobe.com/en_US/FlashPlatform/reference/actionscript/3/

ActionScript 3 Language Specificationhttp://livedocs.adobe.com/specs/actionscript/3/

Twitter@herrodius, @stackandheap Stack & Heap Labshttp://labs.stackandheap.com

Questions ?

Thank you !