javascript : Async/await in .replace

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An easy function to use and understand for some async replace :

async function replaceAsync(str, regex, asyncFn) {
    const promises = [];
    str.replace(regex, (match, ...args) => {
        const promise = asyncFn(match, ...args);
        promises.push(promise);
    });
    const data = await Promise.all(promises);
    return str.replace(regex, () => data.shift());
}

It does the replace function twice so watch out if you do something heavy to process. For most usages though, it’s pretty handy.

Use it like this:

replaceAsync(myString, /someregex/g, myAsyncFn)
    .then(replacedString => console.log(replacedString))

Or this:

const replacedString = await replaceAsync(myString, /someregex/g, myAsyncFn);

Don’t forget that your myAsyncFn has to return a promise.

An example of asyncFunction :

async function myAsyncFn(match) {
    // match is an url for example.
    const fetchedJson = await fetch(match).then(r => r.json());
    return fetchedJson['date'];
}

function myAsyncFn(match) {
    // match is a file
    return new Promise((resolve, reject) => {
        fs.readFile(match, (err, data) => {
            if (err) return reject(err);
            resolve(data.toString())
        });
    });
}

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