How to Execute Promises Sequentially with Array Parameters?

Execute Promises Sequentially with Array Parameters

In some scenarios, you may need to execute promises sequentially, passing parameters from an array. This becomes necessary when the array is populated dynamically and the order of execution is crucial.

One approach to create a "pauseable loop" is by repeatedly using the .then method. However, this can be cumbersome and result in a pyramid-shaped promise chain.

Using Promises

A cleaner solution involves using Array.reduce to fold the promise chain into a single promise:

myArray.reduce(
  (p, x) =>
    p.then(() => myPromise(x)),
  Promise.resolve()
)

This approach creates a series of chained promises, ensuring sequential execution.

Using Async Functions

Alternatively, async functions allow for a more readable and efficient implementation. The following example uses an async function to iterate and execute the promises:

const forEachSeries = async (iterable, action) => {
  for (const x of iterable) {
    await action(x)
  }
}

forEachSeries(myArray, myPromise)

Collecting Return Values

If you need to collect the return values from the promises, you can use a modified version of the forEachSeries function called mapSeries:

const mapSeries = async (iterable, fn) => {
  const results = []

  for (const x of iterable) {
    results.push(await fn(x))
  }

  return results
}

This function iterates through the iterable, collecting the results of the promises and returning an array of the results.

By using these techniques, you can easily execute promises sequentially, passing parameters from an array, ensuring the order of execution and collecting the results as needed.

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