undo/redo with prototype chains

history.js

class HistoryManager {
  constructor(initialState) {
    this.state = { ...initialState };
    this.history = [initialState];
    this.index = 0;
  }

  push(changes) {
    this.state = Object.create(this.state, Object.getOwnPropertyDescriptors(changes));
    this.history.length = this.index + 1; // discard further redos
    this.history.push(this.state);
    this.index++;

    return this.state;
  }

  undo() {
    if (this.index === 0) {
      return;
    }

    this.index--;
    this.state = this.history[this.index];

    return this.state;
  }

  redo() {
    if (this.index === this.history.length - 1) {
      return;
    }

    this.index++;
    this.state = this.history[this.index];

    return this.state;
  }
}

// test
const hist = new HistoryManager({ a: 0 });

hist.push({ a: 1 });
console.assert(hist.state.a === 1);

hist.push({ a: 2 });
hist.push({ a: 3 });
console.assert(hist.state.a === 3);

hist.undo();
hist.undo();
console.assert(hist.state.a === 1);

hist.redo();
console.assert(hist.state.a === 2);

hist.push({ a: Infinity });
console.assert(hist.state.a === Infinity);

hist.redo();
console.assert(hist.state.a === Infinity);