javascript - 在 ES6 之前的 Typescript 中实现 Iterator<T> 的推荐方法

Question

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Answer 1

这是一个副本:typescript: make class objects iterable ，但这是对 ES5 的回答:

您想使用 ES6 feature :

One addition of ECMAScript 2015 (ES6) is not new syntax or a new built-in, but a protocol. This protocol can be implemented by any object respecting some conventions.

There are two protocols: The iterable protocol and the iterator protocol.

在 ES5 环境(编译和/或运行时)中，这不是你能做的。
话虽这么说，你可以足够接近because :

An object is an iterator when it knows how to access items from a collection one at a time, while keeping track of its current position within that sequence. In JavaScript an iterator is an object that provides a next() method which returns the next item in the sequence. This method returns an object with two properties: done and value.

所以你可以只返回一个带有 next 方法的对象，它是一个迭代器:

class Counter /* implements Iterator<number> */ {
    private counter = 0;

    //public next(): IteratorResult<number> {
    public next(): { done: boolean, value: number } {
        return {
            done: false,
            value: this.counter++
        }
    }
}

let c = new Counter();
console.log(c.next().value); // 0
console.log(c.next().value); // 1
console.log(c.next().value); // 2

( code in playground )

注释掉的部分将与目标 ES6 一起工作，但低于它时则不行。
但是，如果您的运行时环境确实支持此功能，那么编译后的 js 就可以很好地完成这项工作。