JS中实现一个串型异步函数队列

// 生成异步请求函数

function genAsyncTask(isSuccess, delay) {
  return (params) => {
    return new Promise((resolve, reject) => {
      setTimeout(() => {
        isSuccess ? resolve(params || 'success') : reject('error')
      }, delay)
    })
  }
}
// 异步请求
const asyncTask1 = genAsyncTask(true, 1000)
const asyncTask2 = genAsyncTask(true, 2000)
const asyncTask3 = genAsyncTask(true, 3000)


// 通常解法
;(async()=>{
let result1 = await asyncTask1('a')
let result2 = await asyncTask2(result1)
await asyncTask3(result2)
// ...
})()

const asyncTasks = [asyncTask3, asyncTask2, asyncTask1]
;(async()=>{
  for(task of asyncTasks){
    console.log(await task())
  }
})()
// 输出：success    3s之后
// 输出：success    再2s之后
// 输出：success    再1s之后

function queuePromises(asyncTasks, initInput = 'initInput') {
  return asyncTasks.reduce(
    (preAsyncTask, curAsyncTask) =>
      preAsyncTask.then((result) => {
        return curAsyncTask(result)
      }),
    Promise.resolve(initInput)
  )
}



;(async () => {
  try {
    let result = await queuePromises([asyncTask1, asyncTask2, asyncTask3])
    console.log(result)
  } catch (error) {
    console.log('error', error)
  }
})()
// 输出：initInput

// 递归解法
function chainPromise(tasks, { limit } = { limit: 3 }) {
  const results = []
  let tryTimes = 1
  let index = 0

  function next() {
    const task = tasks[index]
    if (task) {
      return task().then(
        (result) => {
          tryTimes = 1
          index++
          results.push(result)
          return next()
        },
        (reason) => {
          if (tryTimes <= limit) {
            console.log('try!!!', tryTimes)
            tryTimes++
            return next()
          } else {
            throw new Error('limit more than 3')
          }
        }
      )
    } else {
      return Promise.resolve(results)
    }
  }
  return next()
}
chainPromise([asyncTask1, asyncTask2, asyncTask3]), {limit:3}]).then(console.log)
// [1000,2000,3000]