TypeError: Iterator/AsyncIterator constructor can't be used directly

訊息

TypeError: Abstract class Iterator not directly constructable (V8-based)
TypeError: Iterator constructor can't be used directly (Firefox)
TypeError: Iterator cannot be constructed directly (Safari)

TypeError: Abstract class AsyncIterator not directly constructable (V8-based)
TypeError: AsyncIterator constructor can't be used directly (Firefox)
TypeError: AsyncIterator cannot be constructed directly (Safari)

錯誤型別

哪裡出錯了？

Iterator 和 AsyncIterator 建構函式是抽象類，不應直接使用。它們會檢查 new.target 的值，如果它與建構函式本身相同，則會丟擲錯誤。使用這些建構函式的唯一方法是在子類中繼承它們，並在子類建構函式中呼叫 super()。子類還必須定義一個 next() 方法才能有用。

示例

無效案例

new Iterator();

有效情況

class MyIterator extends Iterator {
  #step;
  #end;
  constructor(start, end) {
    // Implicitly calls new Iterator(), but with a different `new.target`
    super();
    this.#step = start;
    this.#end = end;
  }
  next() {
    if (this.#step >= this.#end) {
      return { done: true };
    }
    return { value: this.#step++, done: false };
  }
}

new MyIterator();

另見

• AsyncIterator
• Iterator