mmoize

A simple cache/single-argument memoization library.

Installation

npm install --save mmoize

API

const mm = mmoize(fn, [options])

Create a new cache instance. The first argument is a function used to create missing value from a key.

• option.size is the maximum cache size
• options.valid({key, value}) a user-defined function invoked after a value has been retrieved from the cache. If this function returns true the cached value is assumed to be still valid. Otherwise, a new value will be obtained by calling fn(key).

Each invocation of the returned function will produce a promise that will be fulfilled either by the value in cache or by the value returned by fn(key).

Newly created values are always stored in the cache. If there isn't enough room left, the least recently used values is discarded.

Example

Basic usage

    const Promise = require('bluebird');
    const mmoize = require('mmoize');
    const assert = require('assert');
    const readFile = Promise.promisify(require("fs").readFile);

    let n = 0;
    const read = mmoize((key) => { n += 1; return readFile(key, "utf8"); });

    // Will actually read the file only once
    read("./test/data/a")
        .then(console.log)
        .then(() => assert.equal(n, 1));

    read("./test/data/a")
        .then(console.log)
        .then(() => assert.equal(n, 1));

    read("./test/data/a")
        .then(console.log)
        .then(() => assert.equal(n, 1));

Concurent access (typically used with promise-returning functions)

    const Promise = require('bluebird');
    const mmoize = require('mmoize');
    const readFile = Promise.promisify(require("fs").readFile);

    const read = mmoize((key) => readFile(key, "utf8"), {size: 3 });

    Promise.all([
        read("./test/data/a"),
        read("./test/data/a"),
        read("./test/data/b"),
        read("./test/data/c"),
        read("./test/data/d"),
        read("./test/data/d"),
        read("./test/data/c"),
        read("./test/data/b"),
        read("./test/data/a"),
    ]).then(console.log);

Node version

Require NodeJS >= v10.0 Tested with v10.0 and v14.15

License

(The MIT License)

Copyright (c) 2018 Sylvain Leroux

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the 'Software'), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED 'AS IS', WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.