rubico/_internal/asyncIteratorReduce.js

[a]synchronous functional programming

/**
 * @name asyncIteratorReduce
 *
 * @synopsis
 * ```coffeescript [specscript]
 * asyncIteratorReduce(
 *   asyncIterator AsyncIterator<T>,
 *   reducer (any, T)=>Promise|any,
 *   result any,
 * ) -> result any
 * ```
 */
const asyncIteratorReduce = async function (asyncIterator, reducer, result) {
  let iteration = await asyncIterator.next()
  if (iteration.done) {
    return result
  }
  if (result === undefined) {
    result = iteration.value
    iteration = await asyncIterator.next()
  }

  while (!iteration.done) {
    result = await reducer(result, iteration.value)
    iteration = await asyncIterator.next()
  }
  return result
}

module.exports = asyncIteratorReduce