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One option is to make a copy of the list of objects at the beginning of each frame, but this could get costly to
do each frame. The best solution is to first mark objects for removal in a separate array and then actually remove
them from the object list after every object has had its turn. Following is the solution GameBoard uses:
// Mark an object for removal
this.remove = function(obj) {
var wasStillAlive = this.removed.indexOf(obj) != -1;
if(wasStillAlive) { this.removed.push(obj); }
return wasStillAlive;
// Reset the list of removed objects
this.resetRemoved = function() { this.removed = []; }
// Remove objects marked for removal from the list
this.finalizeRemoved = function() {
for(var i=0,len=this.removed.length;i<len;i++) {
var idx = this.objects.indexOf(this.removed[i]);
if(idx != -1) {
At the beginning of each step, resetRemoved is called to reset the list of objects to be removed. The re-
move method first checks if an object has already been removed and then adds it to the list of objects to remove
only if it's not already there. It then returns true if the object was added or false if the object was already
dead. After every object has its turn, finalizeRemoved is called. This method finds the removed objects in
the objects list using Array.indexOf and then uses the Array.splice method to cut those objects out of
the list. When an object is removed from the list, it is effectively dead because it no longer has its step and
draw methods called.
Iterating over the List of Objects
Because much of what GameBoard does is iterate over a list of objects, it stands to reason that a couple of
helper methods to make that easier would come in handy. Two main methods are needed. First, a simple iterate
method that calls the same function on every object in the object list is useful for the step and draw methods.
Second, a detect method that returns the first object for which a passed-in function returns true makes col-
lision detection easier. Both of these methods are listed here:
First up is iterate :
// Call the same method on all current objects
this.iterate = function(funcName) {
var args =,1);
for(var i=0,len=this.objects.length;i<len;i++) {
var obj = this.objects[i];
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