onetime

Ensure a function is only called once

When called multiple times it will return the return value from the first call.

Unlike the module once, this one isn't naughty and extending Function.prototype.

This package is a lightweight fork of sindresorhus/onetime that preserves the original behavior and keeps the public API fully compatible, while additionally providing:

• CommonJS support out of the box
• Native TypeScript typings (no separate install)
• Zero runtime dependencies

Install

# pnpm (recommended)
pnpm add @reedchan/onetime

# npm
npm install @reedchan/onetime

# yarn
yarn add @reedchan/onetime

Features

• 🚀 100% API-compatible with the original onetime package
• ⭐ Supports both ESM and CommonJS consumers
• 🔥 Native TypeScript support via included types field
• 🎉 Zero runtime dependencies

Usage

import onetime from '@reedchan/onetime';

let index = 0;

const foo = onetime(() => ++index);

foo(); //=> 1
foo(); //=> 1
foo(); //=> 1

onetime.callCount(foo); //=> 3

import onetime from '@reedchan/onetime';

const foo = onetime(() => {}, {throw: true});

foo();

foo();
//=> Error: Function `foo` can only be called once

API

onetime(fn, options?)

Returns a function that only calls fn once.

fn

Type: Function

The function that should only be called once.

options

Type: object

throw

Type: boolean
Default: false

Throw an error when called more than once.

onetime.callCount(fn)

Returns a number representing how many times fn has been called.

Note: It throws an error if you pass in a function that is not wrapped by onetime.

import onetime from '@reedchan/onetime';

const foo = onetime(() => {});

foo();
foo();
foo();

console.log(onetime.callCount(foo));
//=> 3

fn

Type: Function

The function to get call count from.