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node.js - nodejs，异步在减少，等待不等待承诺解决

问题描述

我不明白为什么所有的承诺都会在同一时间得到解决。我读到它await在循环中不能按预期工作forEach，但它也不能与map任何一个一起工作

const promise = async (ms, name) => {
    return new Promise((resolve, reject) => {
        setTimeout(() => {
            console.log(`resolving ${name}`)
            resolve(name)
        }, ms)
    });
}

async function main() {
    ['foo', 'bar', 'baz'].reduce(async (accum, curr) => {
        const res = await promise(1000, curr)
        return res
    }, Promise.resolve(''))
}

main()

但是 await 在这种情况下可以正常工作：

async function main2() {
    const ms = 1000
    await promise(ms, "foo")
    await promise(ms, "bar")
    await promise(ms, "baz")
}

main2()

标签： node.jsasync-await

解决方案

回调的每次迭代reduce都将同步初始化。在运行回调主体之前，您需要等待上一次迭代中的累加器（幸运的是Promise已经）解决：reduce

const promise = async (ms, name) => {
    return new Promise((resolve, reject) => {
        setTimeout(() => {
            console.log(`resolving ${name}`)
            resolve(name)
        }, ms)
    });
}

async function main() {
    ['foo', 'bar', 'baz'].reduce(async (accum, curr) => {
        // don't progress further until the last iteration has finished:
        await accum;
        const res = await promise(1000, curr)
        return res
    }, Promise.resolve(''))
}

main()

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