Disable a JavaScript function after it runs

Question

I presume it is possible to create a JavaScript function that disables it self after it is done running.

Is possible? How can this effect be achieved?

Can you explain the use case? also what do you mean by disable? — Arun P Johny, Jan 08 '16 at 07:59
do you mean a `javascript function` or do you really want to disable `a javascript` — Jaromanda X, Jan 08 '16 at 07:59
IF you want to run function only once, you should look into `IIFE`. These functions are executed immediately and cannot be called. — Rajesh, Jan 08 '16 at 08:03
Related: [Run javascript function only once](http://stackoverflow.com/q/23859916) — Basilevs, Jan 08 '16 at 08:11

score 4 · Accepted Answer · edited May 23 '17 at 12:15

Wrap arbitrary runnable in following manner:

function once(subject) {
   var first = true;
   return function() {
     if (first) {
        first = false;
        return subject();
     } else {
        return null;
     }
   };
}

var wrapper = once(function() {alert("No more!");});

wrapper(); // alerts
wrapper(); // noop

Runnable will only be executed on first invocation of wrapper.

You can convert a function of arbitrary arguments to an argumentless runnable.

score 2 · Answer 2 · edited May 23 '17 at 12:15

2

something like this?

function a(){ alert(1); a = null;}

invoke a() once, second time it will say

Uncaught TypeError: a is not a function

if the function is anonymous, then make it IIFE

(function(){ alert(1);})();

edited May 23 '17 at 12:15

Community

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1

answered Jan 08 '16 at 08:00

gurvinder372

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1

**Never give up**! :) – void Jan 08 '16 at 08:02
2

Will only work if function is stored in a field of original name. `var b = a; b(); b(); b();` will always alert. – Basilevs Jan 08 '16 at 08:05
1

@Basilevs agree, I guess if OP wants to execute it only once he/she wouldn't want to store its reference in another variable, but good catch! – gurvinder372 Jan 08 '16 at 08:11
@gurvinder372 we can even have named function as IIFEs. They will not be accessible but will add readability to code. – Rajesh Jan 08 '16 at 08:19
@Rajesh `we can even have named function as IIFEs` agree. but `add readability to code` debatable, not totally sure about that. – gurvinder372 Jan 08 '16 at 08:25
If you have multiple `IIFE`s then someone will have to read entire function just to get gist of function. In such cases, name would help. Yes we can add comments, but still I prefer having named IIFEs, even if its just one. – Rajesh Jan 08 '16 at 08:32
@Rajesh agree with readability part. But if one whole file is a function (check jquery source) then it doesn't make sense to name it, right? – gurvinder372 Jan 08 '16 at 08:34
@gurvinder372 Thats true. My point with single function was, if you have an initialize function, you can have a named IIFE there. But if it is used to encapsulate then it will not make much sense. – Rajesh Jan 08 '16 at 08:39
Why do you write `this.a = null` instead of `a = null`? – Barmar Jan 08 '16 at 09:17
@Barmar then it will check variable `a` inside `function a()` and it won't set the function reference to `null`. You can try the same in console. – gurvinder372 Jan 08 '16 at 09:18
If you want to assign to a global variable, it should be `window.a = null;` – Barmar Jan 08 '16 at 09:19
@Barmar true, but what if it is not a global variable? – gurvinder372 Jan 08 '16 at 09:24
Then `this.a` won't work, either, since `this` is `window` unless you're in an object context. – Barmar Jan 08 '16 at 09:31
I just tried `function a() { a = null; }`, `a()` in the console, and after this `a` was null. There's no local binding of the function name inside itself. – Barmar Jan 08 '16 at 09:33
@Barmar you are right. I don't know why `function a(){ alert(1); a = null;}` was alerting earlier multiple times. I have edited my answer. Thanks. – gurvinder372 Jan 08 '16 at 12:50

score 2 · Answer 3 · answered Jan 08 '16 at 08:18

If you want the functionality to be happen only once you can use the following function

function once(fn, context) { 
    var result;

    return function() { 
        if(fn) {
            result = fn.apply(context || this, arguments);
            fn = null;
        }

        return result;
    };
}

// Usage
var canOnlyFireOnce = once(function() {
    console.log('Fired!');
});

canOnlyFireOnce(); // "Fired!"
canOnlyFireOnce(); // nada

Courtesy: https://davidwalsh.name/essential-javascript-functions

score 1 · Answer 4 · answered Jan 08 '16 at 08:01

1

var _flag = true; // Have a flag variable.

function oneTimer(){

     // Check flag is set to true or not
     if(!_flag) return;
     _flag = false;

     // Your function definition here.


}

answered Jan 08 '16 at 08:01

void

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You are using a variable declared in the outer scope of the function, The accepted `once` functional decorator is a much better solution as everything is enclosed within it so there can be no issues with the 'pure' function. Also this would not be reusable, `once` can be used on any function, but if you wanted to do the same thing to another function you would have to do something like `_flag_2` which could get messy quickly. – synthet1c Jan 08 '16 at 11:02

score 1 · Answer 5 · answered Jan 08 '16 at 08:07

As commented, if you want to execute a function only once, you should try IIFE. These functions are invoked immediately and cannot be called afterwards.

Following is a sample code.

(function test() {
  console.log("test");

  (function innerFunc() {
    console.log("Inner Function");
  })();

  try {
    innerFunc();
  } catch (ex) {
    console.log(ex)
  }
})();

try {
  test();
} catch (ex) {
  console.log(ex)
}

score 1 · Answer 6 · answered Jan 08 '16 at 10:27

1

Pretty easy, just assign an empty function to the function:

function once() {
    alert('once');
    once = function () { };
}

once();
once();

answered Jan 08 '16 at 10:27

Nina Scholz

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Disable a JavaScript function after it runs

6 Answers6

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