手写promise

手写promise

class SxPromise{
    static PENDING = 'pending'
    static FULFLED = "success"
    static REJECT = 'failed'
    constructor(fun){
       this.status = SxPromise.PENDING
       this.res = null
       this.fulLIst = []
       this.failLIst = []
       try{
           fun(this.resolve.bind(this),this.reject.bind(this))
       }catch(err){
           this.reject(err)
       }
    }
    resolve(res){
        setTimeout(()=>{
            if(this.status === SxPromise.PENDING){
              this.status = SxPromise.FULFLED
              this.res = res
              this.fulLIst.map(item=>{
                item(res)
              })
            }
        })
    }
    reject(err){
        setTimeout(()=>{
            if(this.status === SxPromise.PENDING){
              this.status = SxPromise.REJECT
              this.res = err
              this.fulLIst.map(item=>{
                  item(err)
              })
            }
        })
    }
    then(success,fail){
        return new SxPromise((resolve,reject)=>{
            success = typeof success === 'function' ? success : ()=>{}
            fail = typeof fail === 'function' ? fail : ()=>{}
            if(this.status === SxPromise.PENDING){
              this.fulLIst.push(success)
              this.failLIst.push(fail)
            }
           if(this.status === SxPromise.FULFLED){
             success(this.res)
           }
           if(this.status === SxPromise.REJECT){
             fail(this.res)
           }
       })
    }
}
console.log('第一次');
let res = new SxPromise((resolve,reject)=>{
    setTimeout(()=>{
        console.log('第二次');
        resolve('resolve。。。。')
        console.log('第三次');
    })
})
res.then((res)=>{
    console.log(res);
}).then((res)=>{
    console.log(11);
})
console.log('第四次');