# onetime [![Build Status](https://travis-ci.org/sindresorhus/onetime.svg?branch=master)](https://travis-ci.org/sindresorhus/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](https://github.com/isaacs/once), this one isn't naughty extending `Function.prototype`.*


## Install

```
$ npm install --save onetime
```


## Usage

```js
let i = 0;

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

foo(); //=> 0
foo(); //=> 0
foo(); //=> 0
```

```js
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`<br>
Default: `false`

Throw an error when called more than once.


## License

MIT © [Sindre Sorhus](https://sindresorhus.com)