arrays - TS | array[n] 返回未定义，数组返回正确

Question

我有一个函数，它将每个键从 Firebase 推送到数组，以便在项目中进一步使用。

// component.ts
let x = this.wordService.getWords();
let randWordList: any[] = new Array();
x.snapshotChanges().subscribe(word => {
  word.forEach(element => {
    randWordList.push(element.key);
 // here it works correct
    console.log(randWordList[0]);
// throw in console -L6VLfqZqj8AeYT_0jwt
  });
});

当我按名称检查控制台整个数组时，它输出正确，但我无权访问随机数组成员。

console.log(randWordList);
// outputs []
//         "0": -L6VLfqZqj8AeYT_0jwt
//          ...
//          length: 8
console.log(randWordList[3]);
// return undefined;
console.log(randWordList["3"]);
// return undefined;

希望有人能帮助我理解我做错了什么。

Answer 1

您声明了 randWordList 变量两次。这使得订阅工作，但随后在回调之外，变量保留了它的空列表的原始值。

更改为:

// component.ts
public someFunction() {
  let x = this.wordService.getWords();
  let randWordList: any[] = new Array();
  x.snapshotChanges().subscribe(word => {
    word.forEach(element => {
      randWordList.push(element.key);
      console.log(randWordList[0]); // => "-L6VLfqZqj8AeYT_0jwt"
    });

    // use randWordList here since it is now populated.

  });

  console.log(randWordList[0]); // => undefined (subscribe callback has not been called) 
}