each.md

npu.each

async function each (
  input: Resolvable<Iterable<Resolvable<any>>>,
  iterator: (item: any, index: number, length: number) => Resolvable<any>,
  options?: {
    inflight?: number = 1
  }
): Promise<any[]>;

Given an Iterable (an array, for example), or a promise of an Iterable, iterates serially over all the values in it, executing the given iterator on each element. If an element is a promise, the iterator will wait for it before proceeding. The iterator function has signature (item, index, length) where value is the current element (or its resolved value if it is a promise).

If, at any step:

• The iterator returns a promise or a thenable, it is awaited before continuing to the next iteration.
• The current element of the iteration is a pending promise, that promise will be awaited before running the iterator.
• The current element of the iteration is a rejected promise, the iteration will stop and be rejected as well (with the same reason).

If all iterations resolve successfully, the .each() call resolves to a new array containing the resolved values of the original input elements.

.each() is very similar to .mapSeries(). The difference between .each() and .mapSeries() is their resolution value. .each() resolves with an array as explained above, while .mapSeries() resolves with an array containing the outputs of the iterator function on each step. This way, .each() is meant to be mainly used for side-effect operations (since the outputs of the iterator are essentially discarded), just like the native Array.forEach() method of arrays, while .map() is meant to be used as an async version of the native Array.map() method of arrays.

Each option: inflight

See Map series option: inflight

Example

const npu = require('native-promise-util')

;(async () => {
  const input = [500, 0, 100, 300, 101]
  const beginMapperOrder = []
  const endMapperOrder = []
  const output = await npu.each(input, async (item) => {
    beginMapperOrder.push(item)
    await npu.delay(item)
    endMapperOrder.push(item)
  }, { inflight: 2 })
  // Print [ 500, 0, 100, 300, 101 ]
  console.log(output)
  // Print [ 500, 0, 100, 300, 101 ]
  console.log(beginMapperOrder)
  // Print [ 0, 500, 100, 101, 300 ]
  console.log(endMapperOrder)
})()