Problem with async/await while using .forEach

Question

I'm making a simple Redis' request which is supposed to return all VALUES (not keys) in my database. The problem is that my function returns tab before the .forEach even starts. Why do I know that? My console.log(tab)'s result is printed before console.log(cards) for each iteration. My interpreter also tells me inside the .forEach function that "Promise returned from forEach argument is ignored". What have I done wrong there? Why isn't async/await working inside .forEach?

router.get("/", async (req, res) => {
    try {
        const keys = await client.keys("*")
        //console.log(result)
        const tab = []
        await keys.forEach(async (key) => {
            const cards = await client.smembers(key)
            console.log(cards)
            tab.push(cards)
        })
        console.log(tab)
        return res.send(tab)
    } catch (err) {
        console.error(err)
    }

});

forEach doesn't return a promise which is why you're getting that warning. — Andy
– Andy, Commented Nov 3, 2021 at 17:31
how about reduce or map? would it work with them? I'd like to avoid using loops — crazyfrog
– crazyfrog, Commented Nov 3, 2021 at 17:37
You'll still be iterating over an array with map or reduce. Maybe create an array of promises and await Promise.all instead. — Andy
– Andy, Commented Nov 3, 2021 at 20:20

Unmitigated · Accepted Answer · 2021-11-03 17:31:29Z

7

forEach is not meant to work with async functions. You can use a for ... of loop instead.

for(const key of keys){
    const cards = await client.smembers(key)
    console.log(cards)
    tab.push(cards)
}

answered Nov 3, 2021 at 17:31

Unmitigated

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3 Comments

crazyfrog Over a year ago

how about reduce or map? would it work with them? I'd like to avoid using loops

Unmitigated Over a year ago

@crazyfrog None of those work with async functions or Promises. Sometimes a simple for loop is the easiest.

Martin Over a year ago

A little further explanation. While the async foreach runs in the original question, the observed outcome is because it's just doing multiple async calls. async will run in parallels with the rest of the logic, which is why he sees that the console.log(tab) is returned before his async foreach. And as noted in this answer, for of is the solution to this problem.

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