1.捕获执行器异常
const MyPromise = require('./myPromise')
let pro = new MyPromise((resolve, reject) => {
throw new Error('executor error')
resolve('hello')
})
pro.then(value => {
console.log(value)
}, reason => {
console.log(reason.message)
})
const PENDING = 'pending' // 等待
const FULFILLED = 'fulfilled' // 成功
const REJECTED = 'rejected'// 失败
class MyPromise {
constructor(executor) {
// 捕获执行器错误
try{
executor(this.resolve, this.reject)
} catch (e) {
this.reject(e)
}
}
status = PENDING
value = undefined
reason = undefined
successCallback = []
failCallback = []
resolve = value => {
if (this.status !== PENDING) return
// 将状态修改为成功
this.status = FULFILLED
// 保存成功之后的值
this.value = value
// this.successCallback && this.successCallback(this.value)
while(this.successCallback.length) {
this.successCallback.shift()(this.value)
}
}
reject = reason => {
if (this.status !== PENDING) return
this.status = REJECTED
this.reason = reason
// this.failCallback && this.failCallback(this.reason)
while(this.failCallback.length) {
this.failCallback.shift()(this.reason)
}
}
then(successCallback, failCallback) {
let promise2 = new MyPromise((resolve, reject) => {
if (this.status === FULFILLED) {
setTimeout(() => {
let x = successCallback(this.value)
// resolve(x)
resolvePromise(promise2, x, resolve, reject)
}, 0)
} else if (this.status === REJECTED) {
failCallback(this.reason)
} else {
// 等待
// 讲成功回调和失败回调进行存储
this.successCallback.push(successCallback)
this.failCallback.push(failCallback)
}
})
return promise2
}
}
function resolvePromise(promise2, x, resolve, reject) {
if (promise2 === x) {
return reject(new TypeError('Chaining cycle detected for promise #<Promise>'))
}
if (x instanceof MyPromise) {
// x.then(value => resolve(value), reason => reject(reason))
x.then(resolve, reject)
} else {
resolve(x)
}
}
module.exports = MyPromise
2.then函数抛出异常
let pro = new MyPromise((resolve, reject) => {
// throw new Error('executor error')
resolve('hello')
})
pro.then(value => {
console.log(value)
throw new Error('then error')
}, reason => {
console.log(reason.message)
}).then(value => {
console.log(value)
}, reason => {
console.log(reason.message)
})
const PENDING = 'pending' // 等待
const FULFILLED = 'fulfilled' // 成功
const REJECTED = 'rejected'// 失败
class MyPromise {
constructor(executor) {
// 捕获执行器错误
try{
executor(this.resolve, this.reject)
} catch (e) {
this.reject(e)
}
}
status = PENDING
value = undefined
reason = undefined
successCallback = []
failCallback = []
resolve = value => {
if (this.status !== PENDING) return
// 将状态修改为成功
this.status = FULFILLED
// 保存成功之后的值
this.value = value
// this.successCallback && this.successCallback(this.value)
while(this.successCallback.length) {
this.successCallback.shift()(this.value)
}
}
reject = reason => {
if (this.status !== PENDING) return
this.status = REJECTED
this.reason = reason
// this.failCallback && this.failCallback(this.reason)
while(this.failCallback.length) {
this.failCallback.shift()(this.reason)
}
}
then(successCallback, failCallback) {
let promise2 = new MyPromise((resolve, reject) => {
if (this.status === FULFILLED) {
setTimeout(() => {
try {
let x = successCallback(this.value)
// 判断x的值是普通值还是promise对象
// 如果是普通值，直接调用resolve
// 如果是promise对象，查看promise对象返回的结果
// 再根据promise对象返回的结果，决定调用resolve还是reject
resolvePromise(promise2, x, resolve, reject)
} catch(e) {
reject(e)
}
}, 0)
} else if (this.status === REJECTED) {
failCallback(this.reason)
} else {
// 等待
// 讲成功回调和失败回调进行存储
this.successCallback.push(successCallback)
this.failCallback.push(failCallback)
}
})
return promise2
}
}
function resolvePromise(promise2, x, resolve, reject) {
if (promise2 === x) {
return reject(new TypeError('Chaining cycle detected for promise #<Promise>'))
}
if (x instanceof MyPromise) {
// x.then(value => resolve(value), reason => reject(reason))
x.then(resolve, reject)
} else {
resolve(x)
}
}
module.exports = MyPromise
3.异步情况的处理
const PENDING = 'pending' // 等待
const FULFILLED = 'fulfilled' // 成功
const REJECTED = 'rejected'// 失败
class MyPromise {
constructor(executor) {
// 捕获执行器错误
try{
executor(this.resolve, this.reject)
} catch (e) {
this.reject(e)
}
}
status = PENDING
value = undefined
reason = undefined
successCallback = []
failCallback = []
resolve = value => {
if (this.status !== PENDING) return
// 将状态修改为成功
this.status = FULFILLED
// 保存成功之后的值
this.value = value
// this.successCallback && this.successCallback(this.value)
while(this.successCallback.length) {
this.successCallback.shift()()
}
}
reject = reason => {
if (this.status !== PENDING) return
this.status = REJECTED
this.reason = reason
// this.failCallback && this.failCallback(this.reason)
while(this.failCallback.length) {
this.failCallback.shift()()
}
}
then(successCallback, failCallback) {
let promise2 = new MyPromise((resolve, reject) => {
if (this.status === FULFILLED) {
setTimeout(() => {
try {
let x = successCallback(this.value)
// 判断x的值是普通值还是promise对象
// 如果是普通值，直接调用resolve
// 如果是promise对象，查看promise对象返回的结果
// 再根据promise对象返回的结果，决定调用resolve还是reject
resolvePromise(promise2, x, resolve, reject)
} catch(e) {
reject(e)
}
}, 0)
} else if (this.status === REJECTED) {
setTimeout(() => {
try {
let x = failCallback(this.reason)
// 判断x的值是普通值还是promise对象
// 如果是普通值，直接调用resolve
// 如果是promise对象，查看promise对象返回的结果
// 再根据promise对象返回的结果，决定调用resolve还是reject
resolvePromise(promise2, x, resolve, reject)
} catch(e) {
reject(e)
}
}, 0)
} else {
// 等待
// 讲成功回调和失败回调进行存储
this.successCallback.push(() => {
setTimeout(() => {
try {
let x = successCallback(this.value)
// 判断x的值是普通值还是promise对象
// 如果是普通值，直接调用resolve
// 如果是promise对象，查看promise对象返回的结果
// 再根据promise对象返回的结果，决定调用resolve还是reject
resolvePromise(promise2, x, resolve, reject)
} catch(e) {
reject(e)
}
}, 0)
})
this.failCallback.push(() => {
setTimeout(() => {
try {
let x = failCallback(this.reason)
// 判断x的值是普通值还是promise对象
// 如果是普通值，直接调用resolve
// 如果是promise对象，查看promise对象返回的结果
// 再根据promise对象返回的结果，决定调用resolve还是reject
resolvePromise(promise2, x, resolve, reject)
} catch(e) {
reject(e)
}
}, 0)
})
}
})
return promise2
}
}
function resolvePromise(promise2, x, resolve, reject) {
if (promise2 === x) {
return reject(new TypeError('Chaining cycle detected for promise #<Promise>'))
}
if (x instanceof MyPromise) {
// x.then(value => resolve(value), reason => reject(reason))
x.then(resolve, reject)
} else {
resolve(x)
}
}
module.exports = MyPromise
let pro = new MyPromise((resolve, reject) => {
// throw new Error('executor error')
// resolve('hello')
// reject('失败')
setTimeout(() => {
resolve('成功。。。')
}, 2000)
})
pro.then(value => {
console.log(value + '1')
// throw new Error('then error')
return 'aaa'
}, reason => {
console.log(reason + '2')
return 10000
}).then(value => {
console.log(value + '3')
})
网友评论