Evaluating a string value into a variable name

[dawsonk]

var spray:Boolean = false;
var count:Boolean = false;
var placement:Boolean = false;

count_mc.addEventListener(MouseEvent.CLICK, doClick, false, 0, true);
placement_mc.addEventListener(MouseEvent.CLICK, doClick, false, 0, true);
spray_mc.addEventListener(MouseEvent.CLICK, doClick, false, 0, true);

function doClick($e:Event):void {
        var btnClicked:String = $e.target.name.substring(0,$e.target.name.indexOf("_mc"));
        this[btnClicked] = ! this[btnClicked];
        trace(this[btnClicked]);
}