A simple promise implementation

simple-promise.js

// https://medium.com/gitconnected/understand-javascript-promises-by-building-a-promise-from-scratch-84c0fd855720

class SimplePromise {
  constructor(executionFunction) {
    this.promiseChain = [];
    this.handleError = () => {};
    
    this.onResolve = this.onResolve.bind(this);
    this.onReject = this.onReject.bind(this);
    
    executionFunction(this.onResolve, this.onReject)
  }
  
  then(onResolve) {
    this.promiseChain.push(onResolve)
    
    return this
  }
  
  onResolve(value) {
     let storedValue = value
     try {
       this.promiseChain.forEach(nextFunction => {
         storedValue = nextFunction(storedValue)
       })
     } catch(err) {
       this.promiseChain = []
       
       this.onReject(error)
     }
  }
  
  catch(errorHandler) {
    this.handleError = errorHandler
    
    return this
  }
  
  onReject(error) {
    this.handleError(error)
  }
}