# onetime [](https://travis-ci.org/sindresorhus/onetime)
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> Ensure a function is only called once
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When called multiple times it will return the return value from the first call.
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*Unlike the module [once](https://github.com/isaacs/once), this one isn't naughty extending `Function.prototype`.*
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## Install
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```
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$ npm install --save onetime
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```
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## Usage
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```js
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let i = 0;
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const foo = onetime(() => i++);
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foo(); //=> 0
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foo(); //=> 0
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foo(); //=> 0
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```
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```js
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const foo = onetime(() => {}, {throw: true});
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foo();
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foo();
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//=> Error: Function `foo` can only be called once
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```
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## API
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### onetime(fn, [options])
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Returns a function that only calls `fn` once.
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#### fn
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Type: `Function`
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Function that should only be called once.
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#### options
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Type: `Object`
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##### throw
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Type: `boolean`<br>
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Default: `false`
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Throw an error when called more than once.
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## License
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MIT © [Sindre Sorhus](https://sindresorhus.com)
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