How do I call a dynamically-named method in Javascript?

Question

I am working on dynamically creating some Javascript that will be inserted into a web page as it's being constructed.

The Javascript will be used to populate a listbox based on the selection in another listbox. When the selection of one listbox is changed it will call a method name based on the selected value of the listbox.

For example:

Listbox1 contains:

Colours
Shapes

If 'Colours' is selected then it will call a "populate_Colours" method that populates another listbox.
To clarify my question: how do I make that "populate_Colours" call in Javascript?

Answer 1

Assuming the 'populate_Colours' method is in the global namespace, you may use the following code, which exploits both that all object properties may be accessed as though the object were an associative array, and that all global objects are actually properties of the window host object.

var method_name = "Colours";
var method_prefix = "populate_";

// Call function:
window[method_prefix + method_name](arg1, arg2);

Answer 2

As Triptych points out, you can call any global scope function by finding it in the host object's contents.

A cleaner method, which pollutes the global namespace much less, is to explicitly put the functions into an array directly like so:

var dyn_functions = [];
dyn_functions['populate_Colours'] = function (arg1, arg2) { 
                // function body
           };
dyn_functions['populate_Shapes'] = function (arg1, arg2) { 
                // function body
           };

This array could also be a property of some object other than the global host object too meaning that you can effectively create your own namespace as many JS libraries such as jQuery do. This is useful for reducing conflicts if/when you include multiple separate utility libraries in the same page, and (other parts of your design permitting) can make it easier to reuse the code in other pages.