ArrayMap.js

class ArrayMap extends Map {
  constructor(...params) {
    super();
    params.forEach(([key, value]) => this.set(key, value));
  }
  set(key, value) {
    const len = key.length;
    const cp = [...key];
    let chn = super.has(len) ? super.get(len) : (super.set(len, new Map),super.get(len));
    let prop = cp.shift();
    do {
      chn = 
        !cp.length ? chn.set(prop, value).get(prop) :
        chn.has(prop) ? chn.get(prop) : chn.set(prop, cp.length ? new Map : value).get(prop);
    } while (prop = cp.shift());
    return this;
  }
  get(key) {
    const len = key.length;
    const cp = [...key];
    let chn = super.has(len) ? super.get(len) : null;
    if (!chn) return;
    let prop = cp.shift();
    do {
      chn = chn.has(prop) ? chn.get(prop) : undefined;
    } while (prop = cp.shift());
    return chn;
  }
  has(key) {
    const len = key.length;
    const cp = [...key];
    let chn = super.has(len) ? super.get(len) : null;
    if (!chn) return false;
    let prop = cp.shift();
    let result = true;
    do {
      chn = chn.has(prop) ? chn.get(prop) : result = false;
    } while ((prop = cp.shift()) && result);
    return result;
  }
}

am = new ArrayMap();
am.set([1,2], 5);
am.set([1,3,5], 7);
am.has([1,2,3]);