Immutability.js as data store with get, set, merge and added undo, redo

immutable-store.js

const STORE = {
  head: new Map(),
  undoStack: [],
  redoStack: [],
  //implement undo
  undo: () => {
    if (STORE.undoStack.length === 1) return STORE.head;
    const action = STORE.undoStack.pop();
    STORE.head = STORE.undoStack[STORE.undoStack.length - 1];
    STORE.redoStack.push(action);
    return action;
  },
  redo: () => {
    if (STORE.redoStack.length === 0) return STORE.head;
    STORE.head = STORE.redoStack.pop();
    STORE.undoStack.push(STORE.head);
    return STORE.head;
  }
};
//push empty map
STORE.undoStack.push(STORE.head);
//functions
['get', 'toJS'].forEach(k => STORE[k] = (...args) => STORE.head[k](...args));
['set', 'merge'].forEach(k => STORE[k] = (...args) => {
  STORE.head = STORE.head[k](...args);
  STORE.undoStack.push(STORE.head);
  STORE.redoStack = [];
});
//tests
STORE.set(0, 'zero');
STORE.set(1, 'one');
console.log(STORE.toJS());
STORE.undo();
console.log(STORE.toJS());
STORE.undo();
console.log(STORE.toJS());
STORE.redo();
console.log(STORE.toJS());
STORE.redo();
console.log(STORE.toJS());
STORE.undo();
STORE.set(2, 'two'); //redo erase
STORE.undo();
STORE.undo();
STORE.undo();
STORE.undo(); //no risk undo
STORE.redo();
STORE.redo();
STORE.redo();
STORE.redo(); //no risk redo
console.log(STORE.toJS()); //{0: "zero", 2: "two"}