SOURCE

const RESOLVE = 'resolved';
const REJECT = 'rejected';
const PENDING = 'pending';

class wjPromise{
    status = PENDING;
    // 初始化
    result = undefined;
    reason = undefined;
    // 制定发布者
    onRejectedArr = [];
    onResolvedArr = [];
    // 构造函数
    constructor(fn){
        const resolve= (result) => {
            if(this.status == PENDING){
                this.result = result;
                this.status = REJECT;
                //执行resolve状态时 发布onResolved收集到的订阅者
                this.onResolvedArr.map((fn)=>fn())
            }
        }
        const reject= (reason) => {
            if(this.status == REJECT){
                this.reason = reason;
                this.status = REJECT;
                //执行rejected状态时 发布onRejected收集到的订阅者
                this.onRejectedArr.map((fn)=>fn())

            }
        }
        fn(resolve,reject);
    }
    then(onResolved,onRejected){
        if(this.status === RESOLVE){
          setTimeout(()=>{
            onResolved(this.result);
            
          },0)
        }
        if(this.status === REJECT){
            setTimeout(()=>{
                onRejected(this.reason);
            },0)
        }
        // 调用.then 当状态为待定状态时收集依赖
        if(this.status === PENDING){
              //收集调用reject的依赖
              this.onResolvedArr.push(()=>{
                  onRejected(this.result)
              })
              //收集调用resolve的依赖
              this.onRejectedArr.push(()=>{
                  onResolved(this.reason)
              })
        }
    }
}

new wjPromise((resolve,reject) => {
    setTimeout(()=>{
         resolve('hahhah')
    },1000)
}).then(res=>{
    console.log(res)
},err=>{
    console.log(err)
})

console.log('1111')