for..of和迭代器状态 [英] for..of and the iterator state

问题描述

考虑此python代码

Consider this python code

it = iter([1, 2, 3, 4, 5])

for x in it:
    print x
    if x == 3:
        break

print '---'

for x in it:
    print x

它打印 1 2 3 --- 4 5 ，因为迭代器 it 会记住整个循环的状态.当我在JS中做同样的事情时，得到的只是 1 2 3 --- .

it prints 1 2 3 --- 4 5, because the iterator it remembers its state across the loops. When I do seemingly the same thing in JS, all I get is 1 2 3 ---.

function* iter(a) {
    yield* a;
}

it = iter([1, 2, 3, 4, 5])

for (let x of it) {
    console.log(x)
    if (x === 3)
        break
}

console.log('---')

for (let x of it) {
    console.log(x)
}

我想念什么?

推荐答案

不幸的是，JS中的生成器对象不可重用.在 MDN

Generator objects in JS are not reusable unfortunately. Clearly stated on MDN

即使for ... of循环是提前终止，例如通过break关键字终止.退出时循环，生成器关闭，并尝试再次对其进行迭代无法产生任何进一步的结果.

Generators should not be re-used, even if the for...of loop is terminated early, for example via the break keyword. Upon exiting a loop, the generator is closed and trying to iterate over it again does not yield any further results.

这篇关于for..of和迭代器状态的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！