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# one-time-execution-method

Define methods that will be executed only once.

For async functions the resulting Promise of the 1st. invocation will be preserved and always delivered in the future.

# example

<!-- skip-example -->

```javascript
import { replaceWithOneTimeExecutionMethod } from "one-time-execution-method";

class MyClass {
  constructor() {
    this.executions = 0;
  }

  initialize() {
    this.executions++;
    return new Promise(resolve => setTimeout(resolve, 1000));
  }
}

// replace initialize() method of MyClass to be executed only once
replaceWithOneTimeExecutionMethod(MyClass.prototype, "initialize");

async doit() {
  const object = new MyClass();

  // start several initializations in parallel
  Promise.all([object.initialize(), object.initialize(), object.initialize()]);

  await object.initialize();

  // even after several parallel executions only one run is done
  console.log(this.executions); // -> 1
}

doit();
```

# API

<!-- Generated by documentation.js. Update this documentation by updating the source code. -->

### Table of Contents

*   [replaceWithOneTimeExecutionMethod](#replacewithonetimeexecutionmethod)
    *   [Parameters](#parameters)
*   [transitionState](#transitionstate)

## replaceWithOneTimeExecutionMethod

Replace a given method with one that will only be executed once.
For async functions the resulting Promise of the 1st. invocation
will be preserved and always delivered in the future.

```js
class MyClass {
  async initialize() {
   // code here will be executed only once
  }
}
replaceWithOneTimeExecutionMethod(MyClass.prototype, "initialize");

const object = new MyClass();
object.initialize(); // body will/can be executed only once
object.initialize(); // 2nd. call immediatly returns
```

### Parameters

*   `object` **[Object](https://developer.mozilla.org/docs/Web/JavaScript/Reference/Global_Objects/Object)** prototype to bind method against
*   `name` **[string](https://developer.mozilla.org/docs/Web/JavaScript/Reference/Global_Objects/String)** of the method

## transitionState

Object symbol slot holding the state of the method.

*   undefined -> call func and store Promise
*   Promise   -> func currently running or fullfilled -> deliver this Promise

# install

With [npm](http://npmjs.org) do:

```shell
npm install one-time-execution-method
```

# license

BSD-2-Clause