How to evaluate a variable so that it is treated like its contents in JavaScript?

Question

Ok, I don't know how to actually ask this question without showing it. (Also explains why I can't figure out how to search for it on Google.)

Given the following like of code:

dijit.byId('leftNavigationPane').onLoad = function(){setSecondaryNav(url.secondaryNavId);};

I want the variable url.secondaryNavId to be evaluated, so what I really want is it to be treated something like this:

dijit.byId('leftNavigationPane').onLoad = function(){ setSecondaryNav('item1'); };

I am sure there is probably a better way to do this, so feel free to suggest something.

Answer 1

There is the JavaScript eval() function.

Answer 2

Don't use eval!

You can use a self-invoking function and closures as follows:

dijit.byId('leftNavigationPane').onLoad = function(id){
    return function(){ setSecondaryNav(id); };
}(url.secondaryNavId); 

This will execute the outer anonymous function immediately (at runtime), passing the url.secondaryNavId parameter, which will then create a closure that the inner anonymous function will use (so id will always contain the assignment-time value of the url.secondaryNavId property).