限制promise操作的并发数

limitPromiseConcurrency.ts

/*
 * 改自 https://github.com/sindresorhus/p-limit
 */ 
 
export function limitPromiseConcurrency<Result = any>(concurrency: number) {
  type FnType = () => Promise<Result>
  type ResolveFn = (r: Result) => void
  type RejectFn = (r: any) => void

  if (concurrency <= 0) {
    throw new TypeError('concurrency must greater than 0')
  }

  const queue: any[] = []
  let activeCount = 0

  const next = () => {
    activeCount--

    const task = queue.shift()
    task?.()
  }

  const run = async (fn: FnType, resolve: ResolveFn, reject: RejectFn) => {
    activeCount++

    const p = fn()

    try {
      const result = await p
      resolve(result)
      next()
    } catch (err: any) {
      // 出现错误时清空队列
      queue.length = 0
      reject(err)
    }
  }

  const enqueue = (fn: FnType, resolve: ResolveFn, reject: RejectFn) => {
    queue.push(run.bind(undefined, fn, resolve, reject))
    ;(async () => {
      await Promise.resolve()

      if (activeCount < concurrency && queue.length > 0) {
        queue.shift()()
      }
    })()
  }

  const generator = (fn: FnType) =>
    new Promise((resolve, reject) => {
      enqueue(fn, resolve, reject)
    })

  return generator
}
  
const limit = limitPromiseConcurrency(2)

const tasks = []
tasks.push(limit( () => { async action } ))
Promise.all(tasks).then(res => {}).catch(error => {})