I am trying to change the definition of a function:
var a = function(){alert('a');};
var b = a;
b = function(){alert('b');};
This results in the variable a keeping it's original assignment i.e. the function producing alert('a').
Is there any way of passing around a reference to a javascript function so that I can alter it later?
Would you expect the value of a to change after the following snippet? Snippet in question:
var a = 10;
var b = a;
var b = 20;
No, right? So why would you expect reassigning b to also affect a?
After line 1, you have a pointing to a function instance:
After line 2, you have a new variable b, also pointing to the same function instance. So now you have two variables, both pointing to the same instance:
After line 3, you have reassigned b to something else (a new function), but a is still pointing to the original function:
You can do what you want by doing something like this:
var func = function() { alert("a"); };
var a = function() { func(); };
var b = a;
func = function() { alert("b"); };
Now calling a() or b() will alert the string b.
20 anywhere; the code is only alerting the string literals a or b.
Is there any way of passing around a reference to a javascript function so that I can alter it later?
There is no way to do this. Javascript does not have "pointers". It has reference values, and as such, a is a reference to the value of a, not to the memory location of a.
So, for this set of instructions
var a = function(){alert('a');};
var b = a;
b = function(){alert('b');};
this is the progression
//a is stored at some memory location
var a;
//b is stored at some memory location
var b;
//the memory location where a is stored has its value updated
a = function(){alert('a');};
//the memory location where b is stored has its value updated
//from the value stored at a's memory location
b = a;
//the memory location where b is stored has its value updated
b = function(){alert('b');};
You could produce the result you're looking for like this:
var fn = function() { alert('a'); };
var a = function() { fn(); };
var b = a;
fn = function(){ alert('b'); };
This code would produce the desired effect you're looking for because they'll both call fn() and you're changing the common underlying reference.
