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Promise/A+ 规范
- 三种状态 pending || fullfiled(resolved) || rejected
- 当处于 pending 状态的时候,可以转移到 fullfiled(resolved) 或者 rejected 状态
- 当处于 fullfiled(resolved) 状态或者 rejected 状态的时候,就不可变
- 必须有一个 then 异步执行方法,then 接收 2 个参数并且必须返回一个 promise:
- onFullfiled 用来接收 promise 成功的值
- onRejected 用语接收 promise 失败的原因
- promise.prototype.then = function(onFullfiled,onRejected){}
面试够用版
function myPromise(constructor) {
let self = this;
self.status = 'pending';
self.value = undefined;
self.reason = undefined;
function resolve(value) {if (self.status === 'pending') {
self.value = value;
self.status = 'resolved'
}
}
function reject(reason) {if (self.status === 'pending') {
self.reason = reason;
self.status = 'rejected'
}
}
try {constructor(resolve, reject)
} catch (e) {reject(e)
}
}
myPromise.prototype.then = function(onFullfiled, onRejected) {
let self = this;
switch (self.status) {
case 'resolved':
onFullfiled(self.value)
break;
case 'rejected':
onRejected(self.reason)
break;
default:
}
}
var p = new myPromise((resolve, reject) => {resolve(1)
})
p.then((x) => {console.log(x)
})
正文完
发表至: javascript
2019-04-24