Using String Variables to Call Functions in AS3

Have you ever wanted to use a string to call a function? What do you mean, you ask? Well let me explain. Let’s say I have a variable called myfunc that is a string with “functionFromVariable” stored in it. Here’s the code:

var myfunc:String = "functionFromVariable";

Nothing too complex huh? Now let’s also say I have a function called functionFromVariable. Here’s its code:

public function functionFromVariable() : void
{
     trace("I was ran from a string");
}

Alright. So now I want to call our functionFromVariable function using our string. From inside our class all I have to do is:

this[myfunc]();

That’s great I know… now why would you ever want to do that? I know, it’s probably rare at best but I’ll give you too crazy off beat examples that could make sense.

Example 1: Calling Functions in a Series

I’ve used this setup before to do exactly what I am about to show you. I wrote a tutorial class once that had a series of functions called: step1, step2, step3, step4, step5 … and so on. Now I didn’t want to keep track of what step I was on as I traveled through the list. See when a step was completed it called a stepCompleted function that went to the next step. Since stepCompleted was used at the end of each step I could not just blatantly call the next step. The solution was simple though, I just needed to attach a number onto step each time.

So what did I do? I created a variable called currentStep that was an int and incremented it at the beginning of stepCompleted each time. Then I could simply call this["step"+currentStep](); to run the next step. So my stepCompleted function looked like this:

public function stepCompleted() : void
{
    currentStep++; // my class variable to track the current step
    this["step"+currentStep](); //call the next function in the series
}

Worked like a charm and called functions step1, step2, step3, and so on until I told it otherwise at the end of the tutorial.

Example 2: Randomly calling Functions to set Enemy Attack Patterns

Let’s say you have an enemy that has four modes of movement: jump, walk, fly, swim. And two different attack modes: defensive, offensive.

Well logically you’d probably control these two things separate from each other. But in our case we want our enemy to act completely different if defensive jump mode than in defensive fly mode. And really, I just want to show you it works, even if this is the stupidest example ever.

So here’s what we can do.

Make two arrays:

var movement:Array = ["jump", "walk", "fly", "swim"];
var attack:Array = ["defensive", "offensive"];

Now let’s say we create a different function for every combination. That’s eight functions, Here’s a list as an example:

jumpdefensive
jumpoffensive
walkdefensive
walkoffensive
flydefensive
flyoffensive
swimdefensive
swimoffensive

So you’ve got these 8 different functions and you want to randomly call one every so often to change to characters mode. All you have to do is randomly select an item from each array and call it with () on the end. Like this:

this[movement[Math.floor(Math.random()*movement.length)]+attack[Math.floor(Math.random()*attack.length)]]();

Yeah that was probably too long and confusing to read. Don’t freak out, here’s a cleaner example:

this[movement[2]+attack[1]]();

So in the directly above case we would be calling this.flyoffensive();

Closing

So that’s pretty much it. I’m sure there are more reasons for using this method, but now that you know how to do it, you’ll be ready to use it when they arise.

About the Author

Par

Hey! Don't be surprised, I'm a flash developer. While Flash is definitely one of my favorite languages to develop in, most of all I just like making games. If you want to see the games I've developed so far head over to my website, DigitallyBold, in the link below. If you want to know more about what I'm working on now and in the future be sure to follow me on twitter.

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