Javascript: Converting a string representation of an object to an actual Object without eval

We all know that eval is evil, right? Every once in a while, I run across a situation where it is very tempting to just use “eval”, but in general I avoid it.

Granted, there are acceptable reasons to use “eval”, but I have a hard time justifying a new instance of the JavaScript compiler just for convenience.  (…Not to mention debugging and scope issues)

I was tempted today by the following scenario:

The application I was working on was providing a series of string values that represented different JavaScript objects/functions (nicely namespaced for once, I mightadd).  Depending on a user’s actions, the values vary.  In order to complete the functionality, I needed these strings to be actual objects.

Here is a simplified example of one of the strings:

‘Company.info.image.upload’ …where the last object (upload) is a function

I could have just:    eval(‘Company.info.image.upload’ + ‘()’);

However, it would be a much cleaner solution if I were able to control the scope of the function/object being called.  So, without using eval, how do you execute a method for which you only have the string representation?

var someString = 'Company.info.image.upload',
arObj = someString.split('.'),
obj = window;
for (var i = 0, len = arObj.length; i < len; i++) { obj = obj[arObj[i]]; }
if (obj !== window) { obj.apply(this); }

//P.S. I love associative arrays in javascript

That’s it!  Build the object in the loop and execute the method using apply().

A couple of quick notes:

  • It is important to keep in mind that eventthough the “upload” method is namespaced, it is still ultimately a child object of the window object. (i.e. Company.info.image.upload is actually window.Company.info.image.upload)
  • Similarly, it is worth noting that I used the apply method so that I could pass in the desired scope

Some informative links:

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