SOURCE

class Promise{
  cbs=[];
  value='';
  status='pending'

  constructor(invoke){
    invoke(this.resolve.bind(this));
  }

  then(call){
    console.log('then')
    if(this.status==='pending'){    
        this.cbs.push(call);
    }else{
        call(this.value)
    }
    return this;
  }

  resolve(value){
    setTimeout(()=>{
        this.status='fulfilled';
        this.value=value;
        console.log('resolve')
        this.cbs.forEach(c=>c(value))
    },0)
  }
}

new Promise((resolve)=>{
    resolve('promise');
}).then((res)=>{
    console.log(res,'then');
}).then((res)=>{
    console.log(res,'then1');
})