Calling a JavaScript function named in a variable

javascript function variables
Matt W picture Matt W · Nov 12, 2009 · Viewed 224k times · Source

I have a JavaScript variable which contains the name of a JavaScript function. This function exists on the page by having been loaded in and placed using $.ajax, etc.

Can anyone tell me how I would call the javascript function named in the variable, please?

The name of the function is in a variable because the URL used to load the page fragment (which gets inserted into the current page) contains the name of the function to call.

I am open to other suggestions on how to implement this solution.

Answer

Nosredna picture Nosredna · Nov 12, 2009

I'd avoid eval.

To solve this problem, you should know these things about JavaScript.

  1. Functions are first-class objects, so they can be properties of an object (in which case they are called methods) or even elements of arrays.
  2. If you aren't choosing the object a function belongs to, it belongs to the global scope. In the browser, that means you're hanging it on the object named "window," which is where globals live.
  3. Arrays and objects are intimately related. (Rumor is they might even be the result of incest!) You can often substitute using a dot . rather than square brackets [], or vice versa.

Your problem is a result of considering the dot manner of reference rather than the square bracket manner.

So, why not something like,

window["functionName"]();

That's assuming your function lives in the global space. If you've namespaced, then:

myNameSpace["functionName"]();

Avoid eval, and avoid passing a string in to setTimeout and setInterval. I write a lot of JS, and I NEVER need eval. "Needing" eval comes from not knowing the language deeply enough. You need to learn about scoping, context, and syntax. If you're ever stuck with an eval, just ask--you'll learn quickly.

Related questions

How do JavaScript closures work?

How would you explain JavaScript closures to someone with a knowledge of the concepts they consist of (for example functions, variables and the like), but does not understand closures themselves? I have seen the Scheme example given on Wikipedia, but …

Read More
Define global variable in a JavaScript function

Is it possible to define a global variable in a JavaScript function? I want use the trailimage variable (declared in the makeObj function) in other functions. <html xmlns="http://www.w3.org/1999/xhtml"> <head id="Head1" runat="…

Read More
What is the scope of variables in JavaScript?

What is the scope of variables in javascript? Do they have the same scope inside as opposed to outside a function? Or does it even matter? Also, where are the variables stored if they are defined globally?

Read More