Javascript Initialization Closure

Question

I'm trying to create javascript closure that will tell me if the function has already been run:

This is what I have so far:

function do()
{
   var isInitialized = function()
   {
     var init = false;

     if (init == false)
     {
       init = true;
       return false;
     }

     return init;
   }

   if (!isInitialized())
   {
     // do stuff
   }
}

My function isInitialized always evaluates to true. I'm like 90% sure I'm not setting the internal variable correctly. How do I fix my code?

just move the `init` variable definition to `do` function, `isInitialized` doesn't currently close anything from the parent scope. — newtover, Jan 21 '12 at 06:18

score 2 · Answer 1 · answered Jan 21 '12 at 06:18

First of all, you can't use do as your function name as that's a keyword.

Secondly, you can attach properties right to your function so you don't need a closure or anything like this:

function f() {
    if(f.initialized)
        return;
    f.initialized = true;
    console.log('Doing things.');
}
f();
f();

That will give you just one "Doing things." in the console.

Demo (run with your JavaScript console open): http://jsfiddle.net/ambiguous/QK27D/

Tom · Accepted Answer · 2012-01-21T06:50:03.830

1

Functions are objects in JavaScript so they can be assigned properties which provides a convenient mechanism for achieving what you want to do:

function doit() {
   if (typeof doit.isInitialized === "undefined") {
     doit.isInitialized = true;
     // do stuff
   }
}

edited Jan 21 '12 at 06:50

answered Jan 21 '12 at 06:18

Tom

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You'd have to change the `do` to something else as `do` is a keyword. – mu is too short Jan 21 '12 at 06:19
I thought that but was just copying Mark's naming. – Tom Jan 21 '12 at 06:22
Thanks, I ended up using this. I didn't think to hard about the method name when I was writing my question. – Mark Jan 21 '12 at 06:52
I know this answer is 9 months old, but hopefully I'll get an answer: Why do you use `doit.isInitialized` and not `this.isInitialized`? Thanks. – pilau Oct 25 '12 at 10:49
@pilau: because if you just say ‘doit()‘, then ‘this‘ inside the function will be ‘window‘ or the local equivalent of the global namespace. – mu is too short Oct 25 '12 at 16:30
@muistooshort I get it now. Then I will have to do this to make it work: `doit.isInitialized.call(doit);`, right? – pilau Oct 25 '12 at 17:06
@pilau: You'd have to `doit.call(doit)` and that's a bit cumbersome. – mu is too short Oct 25 '12 at 17:27
@muistooshort Yes, sorry, this is what I meant. Thank you! – pilau Oct 25 '12 at 18:50

score 0 · Answer 3 · answered Jan 21 '12 at 06:18

0

Try this:

function fn(){
  if (typeof fn.hasrun!='undefined'){return;}
  fn.hasrun=true;
  // do stuff
}

answered Jan 21 '12 at 06:18

Mark Robbins

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score 0 · Answer 4 · edited May 23 '17 at 10:34

0

Every time you call isinitialized, it'll reset all the variables to default, so init will ALWAYS start out false. The values set afterwards are NOT carried over to the next time isInitialiazed is called.

What you want is a 'static' variable, which JS doesn't directly support, but can be simulated as per this answer: Static variables in JavaScript

edited May 23 '17 at 10:34

Community

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answered Jan 21 '12 at 06:20

Marc B

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Javascript Initialization Closure

4 Answers4