promise-chain-executor

Promise Chain Executor

A tool for executing promises in a chain, where the output of previous promises are used to change the behaviour of following promises.

A PromiseSupplier is passed to the Promise Chain Executor, this supplier is responsible for creating a new Promise based on the output from the previous Promise.

This can be demonstrated in a simple form with the following example:

const promiseSupplier = async (previousResult:number|null)=> {
  const newResult = (previousResult ?? 0) + 1
  if (newResult > 9) {
    return null
  }
  return newResult
}

const results = await index.execute<number>(promiseSupplier)
// results: [1,2,3,4,5,6,7,8,9]

This is not a very useful example of the executor, a typical use case for the Promise Chain Executor is when you are calling an API to iterate through some results and you receive an offset ID to continue from.

const promiseSupplier = async (previousOffset:string|null)=> {
  
  const newResults = await callApiForNextResults(previousOffset)
  if (newResults.length === 0) {
    return null; // if we are at the end of the results, return null to terminate the chain
  }
  
  await doSomethingWithResults(newResults)
  
  const lastResult = newResults[newResults.length - 1]
  const newOffset = lastResult.id // update the offset to start from the most recent result
  return newOffset
}

// process results from API by chaining promises together for each new offset
await index.execute<string>(promiseSupplier)

Installation

npm install --save promise-chain-executor