Lockify

Leverage promises to ensure a function doesn't execute concurrently

Most asynchronous functions are fine to run concurrently with themselves. But when they're not—lockify them.

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Lockify takes an async function (or any function that returns a promise), and lets you limit concurrency. By default the maximum concurrency is 1.

Let's say we're getting dog descriptions from an API:

const headers = { Authorization: 'Bearer abc123xyz890' }
function fetchDog(name) {
  const url = `http://example.com/dog/${name}`
  return fetch(url, { headers }).then(res => res.json())
}

const allDogs = Promise.all(
  ['Fido', 'Princess', 'Fluffy'].map(fetchDog)
)

Unfortunately this API doesn't allow your key to fetch more than one dog at a time. Lockify can help with that:

const headers = { Authorization: 'Bearer abc123xyz890' }
function fetchDog(name) {
  const url = `http://example.com/dog/${name}`
  return fetch(url, { headers }).then(res => res.json())
}

const politeFetchDog = lockify(fetchDog)

const allDogs = Promise.all(
  ['Fido', 'Princess', 'Fluffy'].map(politeFetchDog)
)

Or, if you've paid more for the "fetch two dogs at a time" plan with the dog description service:

const politeFetchDog = lockify(fetchDog, 2)