# 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`
Default: `false` Throw an error when called more than once. ## License MIT © [Sindre Sorhus](https://sindresorhus.com)