``
function promise(task) {
// 判断类型函数
const Type = (value) => {
const match = Object.prototype.toString.call(value).match(/(\w+)/g)
return match[1].toLocaleLowerCase()
}
let result = null // 单个任务
let asyncTask = {} // 异步函数保存，触发resolve reject 之后调用
let taskList // 存放参数为数组时完成的任务
let firstTask // 第一个reesolve
let hasReject = false // 出现reject
let firstFn
let resolveCount = 0
const resolve = (res, index = null) => {
resolveCount ++
if(hasReject) return
result = res
if(!firstTask) {
firstTask = res
firstFn && firstFn(firstTask)
}
if(taskList) {
taskList[index] = res
}
if(asyncTask.then) {
if (taskList && resolveCount === task.length){
asyncTask.then(taskList)
}else if(!taskList) {
asyncTask.then(result)
}
}
}
const reject = (res) => {
result = res
hasReject = true
if(asyncTask) {
asyncTask.reject(result)
}
}
const then = (fn) => {
if(hasReject) return
if(result) {
fn(result)
}else {
asyncTask['then'] = fn
}
}
const catchR = (fn) => {
if(result) {
fn(result)
}else {
asyncTask['reject'] = fn
}
}
const first = (fn) => {
firstFn = fn
}
if(Type(task) === 'array') {
taskList = []
task.forEach((fn, index) => {
// 保存调用顺序， 按顺序返回
fn((res) => {
resolve(res, index)
}, reject)
})
}else if (Type(task) === 'function') {
task(resolve, reject)
}
return {
then,
catchR,
first
}
}
const Type = (value) => {
const match = Object.prototype.toString.call(value).match(/(\w+)/g)
return match[1].toLocaleLowerCase()
}
// 功能测试
let time1 = (resolve, reject) => {
setTimeout(() => {
reject('first')
}, 1000);
}
let time2 = (resolve, reject) => {
setTimeout(() => {
resolve('second')
}, 2000);}
let time3 = (resolve, reject) => {
setTimeout(() => {
resolve('third')
}, 3000);
}
let Fp = promise([ time3, time2, time1])
Fp.then(res => {
console.log(res)
})
