Window_update which bitmap is it on?

[Derek Chow]

So on an update function how do I know which variable bar to update? Since I forlooped to create multiple bars. Thanks. The update function will not know which bitmap is which?

for(var i = 0; i < achievementText.length; i++){
        this.createVariableBars(i);
    }

Window_unlockables.prototype.createVariableBars = function(x){
    this._variableBar = new Sprite();

    this.addChild(this._variableBar);
    this.drawBars(x);
};

Window_unlockables.prototype.drawBars = function(x) {
    var lineheight = this.lineHeight();
    var rate = eval(achievementVar[0])/achievementNumber[0];
    this._variableBar.x = this.x + 20;
    this._variableBar.y = lineheight*(x+2);
    this.drawText(achievementText[0],0,lineheight*x,Graphics.boxWidth/3,'left');
    this._variableBar.bitmap = new Bitmap(this.variableBarWidth(),this.variableBarHeight());
    this._variableBar.bitmap.fillRect(0,0,this.variableBarWidth(),this.variableBarHeight(),"#424242");
    this._variableBar.bitmap.fillRect(0,0,rate,this.variableBarHeight(),"green");
};