Javascript 在集合中搜索对象键

Question

是否可以使用 javascript“Set”对象来查找具有特定键的元素？像这样的东西：

 let myObjects = [{"name":"a", "value":0}, {"name":"b", "value":1},{"name":"c", "value":2}];
let mySet = new Set(myObjects);
console.log(mySet.has({"name":"a"}));

原文由 Alexandre Senges 发布，翻译遵循 CC BY-SA 4.0 许可协议

Answer 1

不是那样，那会查找您传入的特定对象，该对象不在集合中。

如果您的起点是对象数组，则根本不需要 Set ，只需 Array.prototype.find ：

 let myObjects = [{"name":"a", "value":0}, {"name":"b", "value":1},{"name":"c", "value":2}];
let found = myObjects.find(e => e.name === "a");
console.log(found);

如果您已经有一个 Set 并想在其中搜索匹配项，则可以直接通过 for-of 使用它的迭代器：

 let myObjects = [{"name":"a", "value":0}, {"name":"b", "value":1},{"name":"c", "value":2}];
let mySet = new Set(myObjects);
let found = undefined; // the `= undefined` is just for emphasis; that's the default value it would have without an initializer
for (const e of mySet) {
  if (e.name === "a") {
    found = e;
    break;
  }
}
console.log(found);

…或通过 Array.from 间接地（重新）创建（the）一个数组，然后使用 find ：

 let myObjects = [{"name":"a", "value":0}, {"name":"b", "value":1},{"name":"c", "value":2}];
let mySet = new Set(myObjects);
let found = Array.from(mySet).find(e => e.name === "a");
console.log(found);

---

如果这是你需要经常做的事情，你可以给自己一个实用函数：

 const setFind = (set, cb) => {
  for (const e of set) {
    if (cb(e)) {
      return e;
    }
  }
  return undefined; // undefined` just for emphasis, `return;`
                    // would do effectively th same thing, as
                    // indeed would just not having a `return`
                    // at at all
}

let myObjects = [{"name":"a", "value":0}, {"name":"b", "value":1},{"name":"c", "value":2}];
let mySet = new Set(myObjects);
let found = setFind(mySet, e => e.name === "a");
console.log(found);

你甚至可以把它放在 Set.prototype 上（确保它是不可枚举的），但要小心与未来添加到 Set 的冲突（ _例如_，如果 Set.prototype 在某些时候得到了 find 方法）。

原文由 T.J. Crowder 发布，翻译遵循 CC BY-SA 3.0 许可协议

Answer 2

您可能只想要一组名称：

  let myObjects = [{"name":"a", "value":0}, {"name":"b", "value":1},{"name":"c", "value":2}];

let map = new Set(myObjects.map(el=>el.name));
console.log(map.has("a"));

如果你想通过名称获取对象，这就是 Map 的用途：

 let myObjects = [{"name":"a", "value":0}, {"name":"b", "value":1},{"name":"c", "value":2}];

let map = new Map(myObjects.map(el=>[el.name,el]));
console.log(map.get("a"));

原文由 Jonas Wilms 发布，翻译遵循 CC BY-SA 3.0 许可协议