JSLint: Using a function before it's defined error

Question

I'm using JSLint to verify most of my external Javascript files, but the largest amount of errors I'm getting is from functions being used before they're defined.

Is this really an issue I should worry about?

It seems Firefox, IE7 and Chrome don't care. Functions like the popular init() (which I use often) normally stick at the top as that makes sense to me (I like to pretend it's analogous to main()) will, according to JSLint, need to be pushed to the bottom of the file.

Answer 1

If you declare functions using the function keyword, you can use them before they're declared. However, if you declare a function via another method (such as using a function expression or the Function constructor), you have to declare the function before you use it. See this page on the Mozilla Developer Network for more information.

Assuming you declare all your functions with the function keyword, I think it becomes a programming-style question. Personally, I prefer to structure my functions in a way that seems logical and makes the code as readable as possible. For example, like you, I'd put an init function at the top, because it's where everything starts from.

Answer 2

As this is the top rated google hit and other people might not be seeing it at first in the jslint tool, there is a option called "Tolerate misordered definitions" that allows you to hide this type of error.

/*jslint latedef:false*/

Answer 3

If you're using jshint you can set latedef to nofunc, which will ignore late function definitions only.

Documentation - http://www.jshint.com/docs/options/#latedef

Example usage:

/* jshint latedef:nofunc */

noop();

function noop() {}

Hope this helps.

Answer 4

From jslint's website (http://www.jslint.com/lint.html), you can read about a /*global*/ directive that allows you to set variables that are assumed to be declared elsewhere.

Here is an example (put this at the top of the file):

/*global var1,var2,var3,var4,var5*/

The :true :false is not actually needed from my experience, but it looks like it's recommended from what I read on the site.

Make sure the initial global statement is on the same line as /*, or else it breaks.

Answer 5

To disable this warning in jshint for all files, place this in your .jshintrc file:

{
   "latedef": false
}

Answer 6

In your .jshintrc file, set:

  "latedef": "nofunc",

Answer 7

it is very unfortunate the latedef option was removed. This is essential when trying to create a 'class' with an interface at the top, ie,

function SomeClass() {
   var self = this;
   self.func = func;

   function func {
      ...
   }
}

This style is very common but does not pass jsLint because func is 'used' before being defined. Having to use global for each 'member' function is a total pain.

Answer 8

You can always declare the offending function at the top

eg: var init;

.... but then you'll have to remove the "var" when you get to the true definition further down:

init = function() { };