JS 中实现一个串型异步函数队列_javascript技巧_

// 生成异步请求函数 /* @param {boolean} isSuccess 是否成功 @param {number} delay 请求返回时间 @return {Promise} promise */ 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

/* reduce @param {array} promises 异步请求函数数组 note: 传入异步函数，它返回 promise。而不是传入 promise 对象。 @initInput (any) initInput 初始参数，作为 reduce 初始值参数 */ function queuePromises(asyncTasks, initInput = 'initInput') { return asyncTasks.reduce( (preAsyncTask, curAsyncTask) => preAsyncTask.then((result) => { return curAsyncTask(result) }), Promise.resolve(initInput) ) } /* 测试用例 */ ;(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]