lodash groupBy is a long sync operation starving all other async operations

Question

I'm using lodash group by on a large array, The operation takes a few minutes, which is starving all other async promisees (since we aren't releasing the context)

Does anyone have suggestions to use a different lib \ modify my use of groupBy to solve this?

Answer 1

Sonce groupBy is just

function groupBy<T, V extends PropertyKey>(
  list: T[], get: (v:T) => V,
): Record<V, T[]> {
  const r = {} as Record<V, T[]>
  for (const el of list) {
    (r[get(el)] ??= []).push(el)
  }
  return r
}

you may easily add an interceptor to wait if it takes too long:

async function groupBy<T, V extends PropertyKey>(
  list: T[], get: (v:T) => V,
): Record<V, T[]> {
  const r = {} as Record<V, T[]>
  let now = performance.now()
  for (const el of list) {
    // if `get` is fast, better to smth like `if (i%100==0)` here
    if (performance.now() - now > 10 /*ms*/) {
      // break the execution
      await new Promise(setTimeout) // or whatever waiting function
      now = performance.now()
    }
    (r[get(el)] ??= []).push(el)
  }
  return r
}