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In-Depth Information
Although the meat of the function is just a loop over t his.objects , the method does have a couple of
interesting JavaScript features.
The first line of the method is a well-known JavaScript hack. The arguments object, which is available in
every method call, contains a list of the arguments passed into that method and is used by methods that accept
varying numbers of arguments. arguments acts in many ways like an array, but it's not an actual array. This is
a shame because in this case you'd like to get all the arguments out except for the first, which is the funcName ,
so that they can be passed on to the function to be called on every object. arguments doesn't have the slice
method, but because JavaScript enables you to take methods and apply them to whatever object you like using
call or apply , the line
var args =,1);
can do just that and turn the arguments object into a proper array starting at the second element. Inside of
the loop the code looks up the method in the object's properties using the square bracket operator and then calls
apply to call that method with whatever the passed in arguments are.
Next is the detect method, which will be used later for collision detection. Its job is to run the same function
on all of a board's objects and return the first object that the function returns true for. In the abstract this
doesn't seem all that useful, but if you need to do collision detection or find a specific object based on certain
parameters, the detect method is useful.
// Find the first object for which func is true
this.detect = function(func) {
for(var i = 0,val=null, len=this.objects.length; i < len; i++) {
if([i])) return this.objects[i];
return false;
detect consists of a loop over the objects and a call to the passed-in function with the object passed in as
the this context. If that function returns true , then the object is returned; otherwise, the functions returns
false after it runs out of objects to compare against.
Defining the Board Methods
Next are the standard board functions, step and draw . Using the methods already defined, these functions
have trivial definitions:
// Call step on all objects and then delete
// any objects that have been marked for removal
this.step = function(dt) {
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