node-fetch-cache/classes/caching/memory_cache.js

const KeyTimeout = require('./key_timeout.js');

module.exports = class MemoryCache {
  constructor(options = {}) {
    this.ttl = options.ttl;
    this.keyTimeout = new KeyTimeout();
    this.cache = {};
  }

  get(key) {
    return this.cache[key];
  }

  remove(key) {
    this.keyTimeout.clearTimeout(key);
    delete this.cache[key];
  }

  set(key, value) {
    this.cache[key] = value;

    if (typeof this.ttl === 'number') {
      this.keyTimeout.updateTimeout(key, this.ttl, () => this.remove(key));
    }
  }
};