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flru [![Build Status](https://travis-ci.org/lukeed/flru.svg?branch=master)](https://travis-ci.org/lukeed/flru)\n\n> A tiny (215B) and fast Least Recently Used (LRU) cache\n\nInternally, two caches are kept. This is because it's far more performant to swap (and maintain) dictionaries than it is to `delete`/purge keys on every read/write interaction. Because of this, `flru` will store `2n` items in memory, where `n` is the [`max`](#max) limit. In practice, this means that with `max=3` and items `(a, b, c)` already written, writing a `d` value ***will not*** automatically purge the `a` key. Instead, `a` _can_ be retrieved, which would move it to the \"active\" cache. It's only when this \"active\" half exceeds the `max` that the \"stale\" half is purged.\n\n> See [Usage](#Usage) for a visual explanation~!\n\nThis implementation is optimized for all-around performance – reads, writes, updates, and evictions.\n\n\nThis module is available in three formats:\n\n* **ES Module**: `dist/flru.mjs`\n* **CommonJS**: `dist/flru.js`\n* **UMD**: `dist/flru.min.js`\n\n\n## Install\n\n```\n$ npm install --save flru\n```\n\n\n## Usage\n\n```js\n// Legend:\n// S => the stale cache\n// A => the active cache\n\nconst flru = require('flru');\n\nlet cache = flru(3); // A=[] S=[]\n\ncache.set('a', 1); // A=[a] S=[]\ncache.set('b', 2); // A=[a,b] S=[]\ncache.set('b', 9); // A=[a,b] S=[]\ncache.set('c', 3); // A=[a,b,c] S=[]\n\ncache.has('a'); //=> true\n\ncache.set('d', 4); // A=[d] S=[a,b,c]\ncache.get('a'); // A=[d,a] S=[a,b,c]\ncache.set('e', 5); // A=[d,a,e] S=[a,b,c]\ncache.get('a'); // A=[d,a,e] S=[a,b,c]\ncache.get('c'); // A=[c] S=[d,a,e]\n\ncache.has('c'); //=> true\ncache.has('b'); //=> false\ncache.has('a'); //=> true\n\ncache.clear(); // A=[] S=[]\n```\n\n\n## API\n\n### flru(max)\nreturn `Object`\n\nInitialize a new `flru` cache instance.\n\n#### max\nRequired: `true`
\nType: `Number`
\nDefault: `1`\n\nThe maximum number of items to maintain – must be a positive, non-zero integer!\n\n> **Important:** The default value is pointless and will result in excessive computation. It's there only to avoid memory leak!\n\n\n### flru.has(key)\nReturn: `Boolean`\n\nCheck if the cache has the given key.\n\n#### key\nType: `String`\n\nThe key name to check.\n\n\n### flru.get(key)\nReturn: `Mixed`\n\nGet the assigned value for a given key. Will return `undefined` if the cache has evicted `key` or never contained it.\n\n#### key\nType: `String`\n\nThe item's unique name / identifier.\n\n\n### flru.set(key, value)\nReturn: `undefined`\n\nPersist an item to the cache by a given `key` name.\n\n#### key\nType: `String`\n\nThe item's unique name / identifier.\n\n#### value\nType: `Mixed`\n\nThe item's value to be cached.\n\n\n### flru.clear(keepOld)\nReturn: `undefined`\n\nReset the cache(s) and counter.\n\n#### keepOld\nType: `Boolean`
\nDefault: `false`\n\nWhen `true`, preserves the stale/outgoing cache.\n\n> **Important:** This is used internally & generally should be ignored!\n\n\n## Benchmarks\n\nYou can find benchmarks in the [`bench`]() directory. They are setup to run one library at a time so that there's no cross-contamination of memory management or Node's runtime caching.\n\n* `set` – writing values into _new_ keys\n* `update` – updating values into _existing_ keys\n* `evict` – writing `2 * limit` keys to the cache, forcing eviction\n\n> Results below are with Node v10.13.0\n\n```\n# set()\nflru x 45,261 ops/sec ±1.63% (94 runs sampled)\nlru-cache x 14,240 ops/sec ±5.70% (85 runs sampled)\ntmp-cache x 8,229 ops/sec ±3.06% (83 runs sampled)\ntiny-lru x 24,415 ops/sec ±2.48% (91 runs sampled)\n\n# get()\nflru x 78,585 ops/sec ±1.70% (98 runs sampled)\nlru-cache x 27,409 ops/sec ±2.64% (93 runs sampled)\ntmp-cache x 6,229 ops/sec ±1.06% (87 runs sampled)\ntiny-lru x 20,313 ops/sec ±2.01% (96 runs sampled)\n\n# has()\nflru x 79,843 ops/sec ±1.35% (97 runs sampled)\nlru-cache x 31,354 ops/sec ±2.87% (90 runs sampled)\ntmp-cache x 813,828 ops/sec ±64.67% (95 runs sampled)\ntiny-lru x 128,250 ops/sec ±3.73% (93 runs sampled)\n\n# update()\nflru x 44,885 ops/sec ±1.86% (95 runs sampled)\nlru-cache x 15,616 ops/sec ±2.46% (94 runs sampled)\ntmp-cache x 8,529 ops/sec ±0.85% (87 runs sampled)\ntiny-lru x 23,060 ops/sec ±2.72% (93 runs sampled)\n\n# evict()\nflru x 8,258 ops/sec ±1.48% (88 runs sampled)\nlru-cache x 1,492 ops/sec ±2.60% (77 runs sampled)\ntmp-cache x 836 ops/sec ±0.59% (95 runs sampled)\ntiny-lru x 2,626 ops/sec ±2.61% (81 runs sampled)\n```\n\n\n## Related\n\n- [tmp-cache](https://github.com/lukeed/tmp-cache) - Full-featured (but slower) alternative, supporting time-sensitive expirations.\n- [`tiny-lru`](https://github.com/avoidwork/tiny-lru) - Same as `tmp-cache` but significantly faster.\n\n\n## License\n\nMIT © [Luke Edwards](https://lukeed.com)\n","_attachments":{},"homepage":"https://github.com/lukeed/flru#readme","bugs":{"url":"https://github.com/lukeed/flru/issues"},"license":"MIT"}