all-with-concurrency.js

const allLimited = (actions, { delay = 0, concurrency = 1 }) =>
  new Promise((s, f) => {
    let i = -1
    const end = actions.length
    const result = Array(end)
    const delayed = delay && (fn => setTimeout(fn, delay))
    async function next(x) {
      if (x >= end) return x - end >= concurrency && s(result)
      try {
        const pause = delay && new Promise(delayed)
        result[x] = await actions[x]()
        pause && (await pause)
        next(++i)
      } catch (err) {
        f(err)
      }
    }
    while (i < concurrency) next(++i)
  })

You have 2 options:

• concurrency limit how many actions are called in parallel
• delay add a delay in ms between each call

Note that you must pass an array of functions, not an array of promises