Custom Promise

CustomPromise.js

export class CustomPromise {
 
  constructor (executor) {
    if (typeof executor !== 'function'){
      throw new Error('You must pass a function')
    }
    // Etat de notre promesse
    let _state = State.PENDING;
    this.setState = setter(_state)
    this.getState = getter(_state)

    // Value représente la valeur actuelle de la promesse une fois résolue
    let _value = null
    this.setValue = setter(_value)
    this.getValue =  getter(_value)

    // Chained concentre l'ensemble des actions a executions à la resolution de la promesse
    let _chained = []
    this.setChained = setter(_chained)
    this.getChained = getter(_chained)

    try {
      executor(resolve, reject);
    } catch (err){
      this.reject(err)
    }
  }

  resolve = res => {
    if (this.getState() !== State.PENDING) {
      return
    }
    const then = res != null ? res.then : null;
    if (typeof then === 'function') {
      return then(resolve, reject);
    }

    this.setState(State.FULFILLED);
    this.setValue(res);

    this.getChained().forEach(({onFulfilled, onRejected}) => { onFulfilled(res) });

    return res;
  }

  reject = reason => {
    if (this.getState() !== State.PENDING) {
      return
    }

    this.setState(State.REJECTED);
    this.setValue(reason);
  }

  then(onFullFiled, onRejected){
    // On retourne une promesse pour pouvoir chainer les .then
    return new CustomPromise((resolve, reject) => {

      const _onFulfilled = res => {
        try {
          resolve(onFulfilled(res));
        } catch (err) {
          reject(err);
        }
      };
      const _onRejected = err => {
        try {
          reject(onRejected(err));
        } catch (_err) {
          reject(_err);
        }
      };


      switch(this.getState()) {
        case State.FULFILLED:
          _onFullFiled(this.getValue());
          break;
        case State.REJECTED:
          _onRejected(this.getValue());
          break;
        default:
          this.setChained(this.getChained().push({ onFulfilled: _onFulfilled, onRejected: _onRejected }))
      }
    })
    

  }

}

const State = Object.freeze({
  REJECTED: Symbol('REJECTED'),
  PENDING: Symbol('PENDING'),
  FULFILLED: Symbol('FULFILLED')
});

const setter = key => val => { key = val}
const getter = key => () => key