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
– newtover, Commented Jan 21, 2012 at 6:18

mu is too short · Accepted Answer · 2012-01-21 06:18:32Z

2

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/

answered Jan 21, 2012 at 6:18

mu is too short

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Comments

Tom · Accepted Answer · 2012-01-21 06:50:03Z

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, 2012 at 6:50

answered Jan 21, 2012 at 6:18

Tom

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8 Comments

mu is too short Over a year ago

You'd have to change the do to something else as do is a keyword.

Tom Over a year ago

I thought that but was just copying Mark's naming.

Mark Over a year ago

Thanks, I ended up using this. I didn't think to hard about the method name when I was writing my question.

pilau Over a year ago

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.

mu is too short Over a year ago

@pilau: because if you just say ‘doit()‘, then ‘this‘ inside the function will be ‘window‘ or the local equivalent of the global namespace.

|

Mark Robbins · Accepted Answer · 2012-01-21 06:18:37Z

0

Try this:

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

answered Jan 21, 2012 at 6:18

Mark Robbins

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Comments

Community · Accepted Answer · 2017-05-23 10:34:17Z

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, 2017 at 10:34

CommunityBot

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answered Jan 21, 2012 at 6:20

Marc B

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