javascript - 如何防止对象/数组突变？

Question

我一直在尝试调试奇怪的问题，我终于弄清楚了为什么会这样。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，我使用它的返回值来更新应用程序状态(redux 模式的自定义实现)。当我通过这个函数发送返回值时:

  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......我已经尝试了几件事:

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

..但它没有用。如何防止 routeDefinitions 数组发生突变？

编辑:我成功重现了 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 };
}

然后 routeDefinitions 不发生变化。其他东西正在改变 routeDefinitions。