Function parameters

Pass by Value

function passPrimitives(xParam:int, yParam:int):void
{
  xParam++;
  yParam++;
  trace(xParam, yParam);
}

var xValue:int = 10;
var yValue:int = 15;

trace(xValue, yValue);          // 10 15
passPrimitives(xValue, yValue); // 11 16
trace(xValue, yValue);          // 10 15

Pass by Reference

function passByRef(objParam:Object):void
{
  objParam.x++;
  objParam.y++;
  trace(objParam.x, objParam.y);
}

var objVar:Object = {x:10, y:15};

trace(objVar.x, objVar.y);  // 10 15
passByRef(objVar);          // 11 16
trace(objVar.x, objVar.y);  // 11 16

The objParam parameter references the same object as the global objVar variable. As you can see from the trace statements in the example, changes to the x and y properties of the objParam object are reflected in the objVar object.