ashwinkumar2438

class PromiseCopy{  
  
  finally( callback ){
    // resolveOrReject : forward current #state.
    // value : forward current #result.
    
    /** curried function to pass Promise.resolve or 
        Promise.reject forward based on current Promise #state. **/
    const commonCallback = ( resolveOrReject ) => ( value ) => {
      const response = callback?.() ;

ashwinkumar2438

class PromiseCopy{
  #handlers = [] ;
  #queued = false ;
  
  #dispatchCallbacks(){
      if( this.#state === states.pending )return ;
      if( this.#queued )return ;

      const method = this.#state === states.fulfilled ? 'success' : 'fail' ; //handler method to call

ashwinkumar2438

class PromiseCopy{
  
  catch( failurecallback ){
        return this.then( undefined, failurecallback ) ;
  }
  
}

ashwinkumar2438

class PromiseCopy{
    
    then( successcallback , failurecallback ){
        return new PromiseCopy( ( resolve, reject ) => { 
            /** 
              1. handlers is an Array which will store success handlers and error handlers.
              2. Each entry will have :
                - success method called with resolved value.
                - failure method called with rejected value.
            */

ashwinkumar2438

class PromiseCopy{

  static reject( reason ){
    // We return a new Promise and pass the reason to reject method if Promise.reject is called directly.
    if( !( this instanceof PromiseCopy ) ) return new PromiseCopy( ( _ , rej ) => rej( reason ) ) ; 
    
    //return if promise is settled.
    if( this.#state !== states.pending )return ;
      
    this.#state = states.rejected ;

ashwinkumar2438

class PromiseCopy{

  static resolve( value ){
     /* 
        1. We return a new Promise and pass the value to resolve method if Promise.resolve is called directly.
        2. The resolve method of executor runs this same code with this instance added. 
     */ 
    if( !( this instanceof PromiseCopy ) ) return new PromiseCopy( res => res( value ) ) ; 
    
    //return if promise is settled.

ashwinkumar2438

const states = {
  pending: 'PENDING',
  fulfilled: 'FULFILLED',
  rejected: 'REJECTED'
}
class PromiseCopy{
  #state = states.pending // initial state of promise
  #result = undefined ; 
  
   constructor( executor ){

ashwinkumar2438

Promise.resolve( 'create a resolved promise' );
//Promise {<fulfilled>: 'create a resolved promise'}
Promise.reject( 'create a rejected promise' );
//Promise {<rejected>: 'create a rejected promise'}

ashwinkumar2438

const error = null ; 
//const error = 'error' ; // change to a truthy value to reject promise.
const promise = new Promise( ( resolve, reject ) => {
    //asynchronous operation 
    setTimeout( () => {
       return error ? reject( error ) : resolve( 'final data' ) ;
    }, 3000 );
} );

// before 3 seconds:

ashwinkumar2438

const Matrix=(id)=>{

    const STATE={
        human_id:id,
        current:'IDLING',
        loaders:[]
    }

    const drive=()=>{
            STATE.loaders.push('driving');