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"}));

Answer 1

不是这样，它会寻找你传入的特定对象，它不在集合中。

如果您的起点是对象数组，则不需要 Set根本就只是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 Set并且想要搜索匹配项，您可以直接通过 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);

...或间接通过Array.from (重新)创建(该)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 (确保它是不可枚举的)，但要注意与 future 添加到 Set 的内容发生冲突(例如，如果 Set.prototype 在某些时候得到了 find 方法，我一点也不感到惊讶)。