JavaScript returning var in for loop

Question

I am trying to understand code which implements canvas/context objects. This code returns an object if the sprite of that object is encountered on the canvas at a specified set of coordinates provided by a mouse button down event (as far as I can tell). Does the following code create an array of objects?

var selObj = getObjectByPixel(mx,my);

and

function getObjectByPixel(x,y) {
  gctx.clearRect(0,0,MaxX,MaxY);
  //alert(levelData.world['ExtraBlockTNT_1'].name);
  for (var objname in levelData.world) {
    var obj = levelData.world[objname];
    var sprd = spriteData[obj.definition];
    if(!sprd) continue;
    var tr = transform(obj.x, obj.y, sprd.data.width, sprd.data.height);

    gctx.save();
    gctx.translate(tr.x,tr.y);      
    gctx.rotate(obj.angle);

    gctx.fillRect(-tr.w/2, -tr.h/2, tr.w, tr.h);
    gctx.restore();
    //console.info(x,y);
    var imageData = gctx.getImageData(x, y, 1, 1);
    if (imageData.data[3] > 0) {
      return obj;
    }
  }
  return null;
}

It would seem to me that the first object in the loop will return if pixel data is encountered. If that is the case, does the loop end (which is what I assume will happen) or does it keep returning objects and store them in selObj

I'm quite confused by this code but the app runs without error so I must not be fully understanding it.

Thanks.

Answer 1

It does not return an array. It returns an object, see: return obj; . You can only return from a function once.

ps if the author of this code was to return an array he would have probably called it: getObjectsByPixel (note the s ).

Answer 2

return always ends the execution and returns to the stack at the point the function was entered.

So that means it is only returning a single object. In order to return an array, the function would have to first create the array, and then return it after the loop has finished.

Answer 3

I finally worked out the dynamic of the block. The loop does only return a single obj (which is what I knew anyway). The logic is, for every object sprite on the canvas, an invisible filled rectangle is created in a overlayed canvas until the mouse click coordinates are within the bounds of one of the rectangles. Then the object that that rectangle was generated from is returned.