for...of 一个迭代器而不关闭它

Question

是否可以在中断循环时使用 for...of 循环迭代器的一部分而不关闭迭代器？

示例：

function* numbers(i=0){
  while(true) yield i++;
}

let nums=numbers();

// this loop prints numbers from 0 to 3
for(const n of nums){
  if(n>3) break;
  console.log(n);
}

// this loop doesn't print anything because `nums` has already been closed
for(const n of nums){
  if(n>10) break;
  console.log(n);
}

我知道我可以在自己调用时通过迭代器 iterator.next()。但我想知道是否可以使用 for...of 语法来做到这一点。

Answer 1

没有。但是，您可以提供一个不将 return() 转发给生成器的包装器：

function unclosed(iterable) {
  return {
    [Symbol.iterator]() {
      const iterator = iterable[Symbol.iterator]();
      return {
        next: iterator.next.bind(iterator),
        return: null,
        throw: null,
      };
    },
  };
}

function* numbers(i=0) {
  try {
    while (true) yield i++;
  } finally {
    console.log('done');
  }
}

const nums = numbers();

// this loop prints numbers from 0 to 3
for (const n of unclosed(nums)) {
  console.log(n);
  if (n == 3) break;
}
// and this one the numbers from 4 to 10, as well as 'done'
for (const n of nums) {
  console.log(n);
  if (n == 10) break;
}

for...of 一个迭代器而不关闭它

for...of an iterator without closing it

javascript

iterator

for-of-loop