` const PENDING = 'PENDING';
const RESOLVED = 'RESOLVED';
const REJECTED = 'REJECTED';
// 对于不太经常更改的变量 定于为常量
function MyPromise(fn){
//存一下this 因为在setTimeout中的resolve 调用中 resolve函数 this指向window
var that = this;
// 初始状态
that.state = PENDING;
//接受的参数
that.value = null;
that.rejectCalbacks = [];
that.resolveCallbacks = [];
function resolve(value){
if(that.state === PENDING){
that.state = RESOLVED;
that.value = value;
that.resolveCallbacks.map( cb => cb(that.value));
}
}
function reject(value){
if(that.state === PENDING){
that.state = REJECTED;
that.value = value;
that.rejectCalbacks.map( cb => cb(that.value));
}
}
try{
fn(resolve,reject);
}catch(e){
reject(this.value);
}
}
MyPromise.prototype = {
constructor:MyPromise,
then(onFulFulled,onRejected){
onFulFulled = typeof onFulFulled === 'function' ? onFulFulled : v => v;
onRejected = typeof onRejected === 'function' ? onRejected : r => {
//直接抛出
throw r;
};
if(this.state === PENDING){
this.rejectCalbacks.push(onRejected);
this.resolveCallbacks.push(onFulFulled);
console.log(this.resolveCallbacks)
}
if(this.state === RESOLVED){
onFulFulled(this.value);
}
if(this.state === REJECTED){
onRejected(this.value);
}
}
}
//调用 参考eventLoop 执行机制
new MyPromise((resolve,reject) => {
// 异步宏任务 最后执行
setTimeout(() => {
if(Math.random() > 0.1){
resolve('成功');
}else{
reject('傻哎');
}
},2000)
})
// Promise.then是微任务 但在这里手动实现 是一个同步任务 这里会将处理函数压入 reject 和resolve 状态数组中
.then( ok => {
console.log(ok)
})
` 原格式在这里，掘金的代码块有点难调
