simple JS (ES5) cache

cache.js

function Cache(n, f) {
  if (!new.target) {
    return new Cache(n, f);
  }
  n = n >= 2 ? n : 2;
  var kv = Object.create(null);
  var ki = Object.create(null);
  var ik = Object.create(null);
  var size = 0;

  function randomInt(n) {
    var limit = Math.floor((0x100000000 - n) / n) * n; // largest multiple of n <= 2^32
    var rnd;
    do {
        // Get 32 random bits
        rnd = (Math.random() * 0x100000000) >>> 0; // equivalent to Math.floor(Math.random() * 4294967296)
    } while (rnd >= limit);
    return rnd % n;
  }
  var has = Object.__proto__.hasOwnProperty.bind(kv);
  function getRandom() {
    if (size === 0) {
      return [undefined, undefined];
    }
    var k = ik[randomInt(size)];
    var item = kv[k];
    return [k, item];
  }
  function del(key) {
    var k = key.toString();
    if (!has(k)) return;
    var deletedIdx = ki[k];
    delete ki[k];
    delete kv[k];
    size--;
    if (deletedIdx !== size) {
      var relocatedKey = ik[size];
      ki[relocatedKey] = deletedIdx;
      ik[deletedIdx] = relocatedKey;
    }
    delete ik[size];
  }
  function doEviction() {
    for (var i=0; i < n; i++) {
      var randomPair = getRandom();
      var k = randomPair[0];
      var v = randomPair[1];
      if (k === undefined) return;
      if (!f(k, v)) del(k);
    }
  }
  function get(key) {
    return kv[key.toString()];
  }
  function set(key, value) {
    var k = key.toString();
    var found = has(k);
    kv[k] = value;
    if (!found) {
      // new element added, link it
      ik[size] = key;
      ki[key] = size;
      size++;
      doEviction();
    }
  }
  this.get = get;
  this.set = set;
  this.has = has;
  this.delete = del;
  this.getRandom = getRandom;
  Object.defineProperty(this, 'size', {
    get: function () {
        return size;
    },
    enumerable: true,
  });

  Object.freeze(this);
}