A Model with undo and redo stacks

model.js

const copyObject = (source) => Object.assign({}, source);

const Stack = () => {
  const array = [];
      
  return {
    push (value) {
      array.push(value);
    },
    pop () {
      return array.pop();
    },
    isEmpty () {
      return !array.length;
    }
  };
};

const Model = function (initialAttributes) {
  let redoStack = Stack(),
    attributes = copyObject(initialAttributes || {});
  
  const undoStack = Stack(),
    obj = {
      set (attrsToSet) {
        undoStack.push(copyObject(attributes));
        if (!redoStack.isEmpty()) {
          redoStack = Stack();
        }
        for (let key in (attrsToSet || {})) {
          attributes[key] = attrsToSet[key];
        }
        return obj;
      },
      undo () {
        if (!undoStack.isEmpty()) {
          redoStack.push(copyObject(attributes));
          attributes = undoStack.pop();
        }
        return obj;
      },
      redo () {
        if (!redoStack.isEmpty()) {
          undoStack.push(copyObject(attributes));
          attributes = redoStack.pop();
        }
        return obj;
      },
      get (key) {
        return attributes[key];
      },
      has (key) {
        return attributes.hasOwnProperty(key);
      },
      attributes () {
        return copyObject(attributes);
      }
    };  
  return obj;
};

// usage
const model = Model();
model.set({"who": "Hartnell"});
model.set({"who": "Troughton"});
console.log(model.get("who"));
model.undo();
console.log(model.get("who"));
model.redo();
console.log(model.get("who"));
model.set({"who": "Pertwee"});
console.log(model.get("who"));
model.set({"who": "Baker"});
console.log(model.get("who"));
model.undo();
console.log(model.get("who"));
model.undo();
console.log(model.get("who"));
model.redo();
console.log(model.get("who"));
model.redo();
console.log(model.get("who"));