Using async-await with arr.map()

#javascript #node #programming #beginners

While working on a task today, I had to populate my array of objects using my database.

Instinctively, I used the map function. The code looked something like this:

const dataList = [
    { type: "test__1" },
    { type: "test__2" },
    { type: "test__3" },
    { type: "test__4" }
];

const modifiedList = dataList.map(async (item) => {
    // Get additional properties from DB
    const dataFromDB = await DataModel.findOne({
        type: item.type
    });

    return { ...item, dataFromDB };
});

❗️ Did you spot the error?

👉🏽 In dataList.map(), we are returning an array of promises and not an array.
👉🏽 Hence, the modifiedList will look something like this:

⚡️ The Solution?

Simple! We just need to wrap our function with await Promise.all so that our array of promises is resolved to the desired modifiedList .

const modifiedList = await Promise.all(
    dataList.map(async (item) => {
        // Get additional properties from DB
        const dataFromDB = await DataModel.findOne({
            type: item.type
        });

        return { ...item, dataFromDB };
    });
);

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