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.

Install

$ npm install onetime

Usage

const onetime = require('onetime');

let i = 0;

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

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

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

const onetime = require('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

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.

const onetime = require('onetime');

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

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

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

fn

Type: Function

Function to get call count from.

onetime for enterprise

Available as part of the Tidelift Subscription.

The maintainers of onetime and thousands of other packages are working with Tidelift to deliver commercial support and maintenance for the open source dependencies you use to build your applications. Save time, reduce risk, and improve code health, while paying the maintainers of the exact dependencies you use. Learn more.