ActionScript

• An object oriented programming language used to create interactive content on web pages.
• Somewhat similar in syntax to JavaScript, Java, C++.
• It requires a Flash player plug-in.
• Created by Macromedia who is now part of Adobe.
• Popular for multimedia content on the web.
• A program is composed of a sequence of instructions, usually contains definitions of data types, classes, functions (routines).
• A web-based program is usually event-driven (when the user does this, the following should happen).
• A good introduction.

More about ActionScript

• The ActionScript code resides in action panels.
• The action panels are attached to Frames, Buttons, or Movie Clips. The code in a panel attached to a frame, button or clip controls its behavior.
• Many of the programs are called "movies".
• Files related to a program:
• .fla - flash source code (project) and resources
• .swf - compiled flash file, can be played by the Flash player, but the source code cannot be retrieved from it (some special programs exists that can decompile it).

Programming Basics

• Variables - names for places in the memory that can store values.
• Example:
  var name:String = "John";
• This declares a variable called name of type String (sequence of characters) and containing the value "John".
• The variable name is an identifier. It can be used later to retrieve the value stored in the variable.
• The value of the variable can be changed later:
  name = "Bill";

Control Structures

• Instructions designed to control the execution flow of the program.
• Conditional: executing something under some condition:
  if (x != "food") { dontEat(x); }
• dontEat is a function containing a description of some action to be taken. It depends on a parameter that here has the value of the variable x.
• This function is called only if the value stored in the variable x is not "food".
• The curly braces { } are used to group together instructions (block).

Loops

• Allow the repetition of some instructions while some condition is true or for a given number of times.

  for (i=0; i<7; i++) {
    if (found == false) {
      gameover = false; 
    }
  }

• This loop repeats an action for exactly 7 times.
• i++ increases the value of the variable i by one.
• the == operator checks if two values are equal. Not to be mistaken for the single = which changes the value of a variable.

While Loops

• Second type of universal loop. Execute something while a condition is true:

  var x = 1; 
  while (x <= 5) { 
    trace (x); 
    x = x + 1; 
  }

• This one can be rewritten as

  for (x=1; x<=5; x++) {
    trace(x);
  }

Functions

• Allow us to group together code that is likely to be repeated, identify it by a name, and be able to run it on the base of some parameters or arguments.

  function displayArea (width, height) { 
    trace(width * height); } 

• This declares a function named displayArea, with two arguments width and height.
• trace is an alert that opens a little window displaying its argument.
• To run a function you must do a function call:
  displayArea(10, 20);

Events

• An ActionScript program has to be able to react to what the user is doing. Example.

  on (release) {
    if (words._visible == true) {
      setProperty(words, _visible, false);
    } 
    else {
      setProperty(words, _visible, true);
    }
  }

• words is a more complex variable pointing to an object (image) to be displayed on the web page. It has a property that allows it to be visible or not.
• release is an event generated by the release of the mouse button.
• on (event) is a special syntax that defines behavior related to an event.