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手摸手实现Promise 助力基础(二) -- promise.all -- 面试

是她丫 2022-02-11 阅读 80

peomise.all

  • 接收一个Promise数组,数组中如有非Promise项,则此项当做成功
  • 如果所有Promise都成功,则返回成功结果数组
  • 如果有一个Promise失败,则返回这个失败结果
    static all(promises) {
        const result = []
        let count = 0
        return new MyPromise((resolve, reject) => {
            const addData = (index, value) => {
                result[index] = value
                count++
                if (count === promises.length) resolve(result)
            }
            promises.forEach((promise, index) => {
                if (promise instanceof MyPromise) {
                    promise.then(res => {
                        addData(index, res)
                    }, err => reject(err))
                } else {
                    addData(index, promise)
                }
            })
        })
    }

promise.race

  • 接收一个Promise数组,数组中如有非Promise项,则此项当做成功
  • 哪个Promise最快得到结果,就返回那个结果,无论成功失败
    static race(promises) {
        return new MyPromise((resolve, reject) => {
            promises.forEach(promise => {
                if (promise instanceof MyPromise) {
                    promise.then(res => {
                        resolve(res)
                    }, err => {
                        reject(err)
                    })
                } else {
                    resolve(promise)
                }
            })
        })
    }

promise.allSettled

  • 接收一个Promise数组,数组中如有非Promise项,则此项当做成功
  • 把每一个Promise的结果,集合成数组,返回
    static allSettled(promises) {
        return new Promise((resolve, reject) => {
            const res = []
            let count = 0
            const addData = (status, value, i) => {
                res[i] = {
                    status,
                    value
                }
                count++
                if (count === promises.length) {
                    resolve(res)
                }
            }
            promises.forEach((promise, i) => {
                if (promise instanceof MyPromise) {
                    promise.then(res => {
                        addData('fulfilled', res, i)
                    }, err => {
                        addData('rejected', err, i)
                    })
                } else {
                    addData('fulfilled', promise, i)
                }
            })
        })
    }

promise.any

  • 接收一个Promise数组,数组中如有非Promise项,则此项当做成功
  • 如果有一个Promise成功,则返回这个成功结果
  • 如果所有Promise都失败,则报错
    static any(promises) {
        return new Promise((resolve, reject) => {
            let count = 0
            promises.forEach((promise) => {
                promise.then(val => {
                    resolve(val)
                }, err => {
                    count++
                    if (count === promises.length) {
                        reject(new AggregateError('All promises were rejected'))
                    }
                })
            })
        })
    }
}

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