ES6 类方法在 forEach 循环中不返回任何内容

2022-01-19 00:00:00 function return javascript ecmascript-6 arrow-functions

由于某种原因，PollClass 中的方法 getTwo() 不会返回 2，而是返回 undefined.如果我将 return 语句放在 .forEach() 循环之外，则会返回一个值.

For some reason the method getTwo() inside the PollClass won't return 2 but undefined. If I put the return statement outside the .forEach() loop a value does get returned however.

class Poll {
  constructor(name) {
    this.name = name;
    this.nums = [1, 2, 3];
  }

  getTwo() {
    this.nums.forEach(num => {
      if (num === 2) return num;
    })
  }
}

const newPoll = new Poll('random name');
console.log(newPoll.getTwo()); // returns undefined, not 2

这是闭包、ES 6 的问题还是其他问题?

Is this an issue with closure, ES 6, or a whole other issue?

推荐答案

箭头函数还是函数，你只是从forEach回调函数返回，不是从getTwo，你必须从返回getTwo 函数也是如此.

An arrow function is still a function, and you're only returning from the forEach callback function, not from getTwo, you have to return from the getTwo function as well.

尚不清楚为什么要使用循环以这种方式检查某些内容，但概念类似于

It's not quite clear why you would use a loop to check for something in that way, but the concept would be something like

getTwo() {
    var n = 0;
    this.nums.forEach(num => {
      if (num === 2) n = num;
    })
    return n; // returns something from getTwo()
  }

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