关于前端:BFEdev前端刷题-33-实现PromiseallSettled

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题目33

BFE.dev#33 实现Promise.allSettled()

剖析

和Promise.all()不同，Promise.allSettled()即便是遇到rejection也会期待所有的promise到最初。所以咱们只须要用一个array记录各个promise的fulfill或者reject后果即可。

代码

首先实现根本的new Promise构造。

function allSettled(promises) {
 
  return new Promise((resolve, reject) => {
    const result = []
    
    promises.forEach((promise, index) => {
      promise.then((value) => {
        result[index] = {
          status: 'fulfilled',
          value
        }
      }, (reason) => {
        result[index] = {
          status: 'rejected',
          reason
        }
      })
    })
  })
}

为了检测最终settle的机会，须要一个计数器。同时也留神传入的数据并不一定全副是Promise。

function allSettled(promises) {
  if (promises.length === 0) return Promise.resolve([])
  
  const _promises = promises.map(
    item => item instanceof Promise ? item : Promise.resolve(item)
    )
  
  return new Promise((resolve, reject) => {
    const result = []
    let unSettledPromiseCount = _promises.length
    
    _promises.forEach((promise, index) => {
      promise.then((value) => {
        result[index] = {
          status: 'fulfilled',
          value
        }
        
        unSettledPromiseCount -= 1
        // resolve after all are settled
        if (unSettledPromiseCount === 0) {
          resolve(result)
        }
      }, (reason) => {
        result[index] = {
          status: 'rejected',
          reason
        }
        
        unSettledPromiseCount -= 1
        // resolve after all are settled
        if (unSettledPromiseCount === 0) {
          resolve(result)
        }
      })
    })
  })
}

通过撒花

感激浏览，心愿有所帮忙。有趣味能够本人试试。