如何防止object/array突变？

Question

我一直在尝试调试奇怪的问题，我终于弄明白了为什么会这样。只是不确定如何防止它（；我有这个功能：

getInfo(id) {
  id = id || "zero";
  let i = routeDefinitions.findIndex(r => Boolean(r.name.toLowerCase().match(id)));
  // console.log(i) - works in plunker
  // but in my app sometimes returns -1...
  let current = routeDefinitions[i];
  let next = routeDefinitions[i + 1] ? routeDefinitions[i + 1] : false;
  let prev = routeDefinitions[i - 1] ? routeDefinitions[i - 1] : false;
  return { prev, current, next };
}

..它在 this plunker 中完美运行，但在我的应用程序中，我使用它的 return 值来更新应用程序状态（redux 模式的自定义实现）。当我通过此函数发送 return 值时：

  private _update(_old, _new) {
    let newState = Object.keys(_new)
      .map(key => {
        if (_old[key] === undefined) {
          _old[key] = _new[key];
        } else if (typeof _new[key] === "object") {
          this._update(_old[key], _new[key]);
        } else {
          _old[key] = _new[key];
        }
        return _old;
      })
      .find(Boolean);

    return Object.assign({}, newState || _old);
  }

..routeDefinitions 数组发生了变化，事情开始崩溃了……我尝试了一些事情：

let current = [...routeDefinitions][i];
// and:
return Object.assign({}, { prev, current, next });

..但是没有用。如何防止 routeDefinitions 数组发生突变？

编辑：我已经成功重现了 this plunker

中的错误

Answer 1

routeDefinitions array is mutated and things start to break

如果你的函数是真的：

getInfo(id) {
  id = id || "zero";
  let i = routeDefinitions.findIndex(r => Boolean(r.name.toLowerCase().match(id)));
  // console.log(i) - works in plunker
  // but in my app sometimes returns -1...
  let current = routeDefinitions[i];
  let next = routeDefinitions[i + 1] ? routeDefinitions[i + 1] : false;
  let prev = routeDefinitions[i - 1] ? routeDefinitions[i - 1] : false;
  return { prev, current, next };
}

则routeDefinitions不变异。其他东西正在改变 routeDefinitions。

Answer 2

我通过像这样修改 _update() 解决了这个问题：

  private _update2(_old, _new) {
    let newState = {}; 
    Object.keys(_new)
      .map(key => {
        if (_old[key] === undefined) {
          newState[key] = _new[key];
        } else if (typeof _new[key] === "object") {
          newState[key] = this._update2(_old[key], _new[key]);
        } else {
          newState[key] = _new[key];
        }
        return newState;
      })
      .find(Boolean);

    return Object.assign({}, _old, newState);
  }

我用old state只是为了检查值，等_update()完成后再修改它。

Plunker

如何防止object/array突变？

How to prevent object/array mutation?

javascript

typescript

immutability

angular

angular2-routing