this

References an object or movie clip instance. When a script executes, this references the movie clip instance that contains the script. When a field is called, this contains a reference to the object that contains the called field.

Inside an on() event handler attached to a button, this refers to the Timeline that contains the button. Inside an onClipEvent() event handler attached to a movie clip, this refers to the Timeline of the movie clip itself.

Because this is evaluated in the context of the script that contains it, you can't use this in a script to refer to a variable defined in a class file. Create ApplyThis.as, and enter the following code:

class ApplyThis {
var str:String = "Defined in ApplyThis.as";
function conctStr(x:String):String {
return x+x;
}
function addStr():String {
return str;
}
}

Then, in a FLA or AS file, add the following ActionScript:

var obj:ApplyThis = new ApplyThis();
var abj:ApplyThis = new ApplyThis();
abj.str = "defined in FLA or AS";
trace(obj.addStr.call(abj, null)); //output: defined in FLA or AS
trace(obj.addStr.call(this, null)); //output: undefined
trace(obj.addStr.call(obj, null)); //output: Defined in applyThis.as

Similarly, to call a function defined in a dynamic class, you must use this to invoke the function in the proper scope:

// incorrect version of Simple.as
/*
dynamic class Simple {
function callfunc() {
trace(func());
}
}
*/
// correct version of Simple.as
dynamic class simple {
function callfunc() {
trace(this.func());
}
}

Inside the FLA or AS file, add the following ActionScript:

var obj:Simple = new Simple();
obj.num = 0;
obj.func = function() {
return true;
};
obj.callfunc();
// output: true

You get a syntax error when you use the incorrect version of Simple.as.

Example

In the following example, the keyword this references the Circle object:

function Circle(radius:Number):Void {
 this.radius = radius;
 this.area = Math.PI*Math.pow(radius, 2);
}
var myCircle = new Circle(4);
trace(myCircle.area);

In the following statement assigned to a frame inside a movie clip, the keyword this references the current movie clip.

// sets the alpha property of the current movie clip to 20
this._alpha = 20;

In the following statement inside a MovieClip.onPress handler, the keyword this references the current movie clip:

this.square_mc.onPress = function() {
 startDrag(this);
};
this.square_mc.onRelease = function() {
 stopDrag();
};

See also

Constants, onClipEvent handler