One-time NPM | npm.io

one-time

Call the supplied function exactly one time. This prevents double callback execution. This module can be used on both Node.js, React-Native, or browsers using Browserify. No magical ES5/6 methods used unlike the once module does (except for the async version).

Installation

This module is published to the public npm registry and can be installed by running:

npm install --save one-time

Usage (normal)

Simply supply the function with the function that should only be called one time:

var one = require('one-time');

function load(file, fn) {
  fn = one(fn);

  eventemitter.once('load', fn);
  eventemitter.once('error', fn);

  // do stuff
  eventemitter.emit('error', new Error('Failed to load, but still finished'));
  eventemitter.emit('load');
}

function example(fn) {
  fn = one(fn);

  fn();
  fn('also receives all arguments');
  fn('it returns the same value') === 'bar';
  fn('never');
  fn('gonna');
  fn('give');
  fn('you');
  fn('up');
}

example(function () {
  return 'bar'
});

Usage (async)

The same pattern is available for async functions as well, for that you should import that one-time/async version instead. This one is optimized for async and await support. It following exactly the same as the normal version but assumes it's an async function () {} that it's wrapping instead of a regular function, and it will return an async function() {} instead of a regular function.

import one from 'one-time/async';

const fn = one(async function () {
  return await example();
});

await fn();
await fn();
await fn();

Why not `once`?

The main reason is that once cannot be used in a browser environment unless it's ES5 compatible. For a module as simple as this I find that unacceptable. In addition to that it super heavy on the dependency side. So it's totally not suitable to be used in client side applications.

In addition to that we make sure that your code stays easy to debug as returned functions are named in the same way as your supplied functions. Making heap inspection and stack traces easier to understand.