# ylru
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[![NPM version][npm-image]][npm-url]
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[![build status][travis-image]][travis-url]
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[![Test coverage][codecov-image]][codecov-url]
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[![David deps][david-image]][david-url]
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[![Known Vulnerabilities][snyk-image]][snyk-url]
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[![npm download][download-image]][download-url]
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[npm-image]: https://img.shields.io/npm/v/ylru.svg?style=flat-square
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[npm-url]: https://npmjs.org/package/ylru
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[travis-image]: https://img.shields.io/travis/node-modules/ylru.svg?style=flat-square
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[travis-url]: https://travis-ci.org/node-modules/ylru
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[codecov-image]: https://img.shields.io/codecov/c/github/node-modules/ylru.svg?style=flat-square
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[codecov-url]: https://codecov.io/github/node-modules/ylru?branch=master
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[david-image]: https://img.shields.io/david/node-modules/ylru.svg?style=flat-square
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[david-url]: https://david-dm.org/node-modules/ylru
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[snyk-image]: https://snyk.io/test/npm/ylru/badge.svg?style=flat-square
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[snyk-url]: https://snyk.io/test/npm/ylru
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[download-image]: https://img.shields.io/npm/dm/ylru.svg?style=flat-square
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[download-url]: https://npmjs.org/package/ylru
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**hashlru inspired**
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[hashlru](https://github.com/dominictarr/hashlru) is the **Simpler, faster LRU cache algorithm.**
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Please checkout [algorithm](https://github.com/dominictarr/hashlru#algorithm) and [complexity](https://github.com/dominictarr/hashlru#complexity) on hashlru.
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ylru extends some features base on hashlru:
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- cache value can be **expired**.
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- cache value can be **empty value**, e.g.: `null`, `undefined`, `''`, `0`
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## Usage
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```js
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const LRU = require('ylru');
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const lru = new LRU(100);
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lru.set(key, value);
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lru.get(key);
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// value2 will be expired after 5000ms
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lru.set(key2, value2, { maxAge: 5000 });
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// get key and update expired
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lru.get(key2, { maxAge: 5000 });
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```
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### API
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## LRU(max) => lru
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initialize a lru object.
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### lru.get(key[, options]) => value | null
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- `{Number} options.maxAge`: update expire time when get, value will become `undefined` after `maxAge` pass.
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Returns the value in the cache.
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### lru.set(key, value[, options])
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- `{Number} options.maxAge`: value will become `undefined` after `maxAge` pass.
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If `maxAge` not set, value will be never expired.
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Set the value for key.
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### lru.keys()
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Get all unexpired cache keys from lru, due to the strategy of ylru, the `keys`' length may greater than `max`.
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```js
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const lru = new LRU(3);
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lru.set('key 1', 'value 1');
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lru.set('key 2', 'value 2');
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lru.set('key 3', 'value 3');
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lru.set('key 4', 'value 4');
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lru.keys(); // [ 'key 4', 'key 1', 'key 2', 'key 3']
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// cache: {
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// 'key 4': 'value 4',
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// }
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// _cache: {
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// 'key 1': 'value 1',
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// 'key 2': 'value 2',
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// 'key 3': 'value 3',
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// }
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```
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## License
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[MIT](LICENSE)
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