readme.md•1.96 kB
# onetime [](https://travis-ci.com/github/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 and extending `Function.prototype`.*
## Install
```
$ npm install onetime
```
## Usage
```js
const onetime = require('onetime');
let i = 0;
const foo = onetime(() => ++i);
foo(); //=> 1
foo(); //=> 1
foo(); //=> 1
onetime.callCount(foo); //=> 3
```
```js
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`.
```js
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.
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