A simple JavaScript Promise implementation for education purposes

PromiseSimple.js

class PromiseSimple {
  constructor(executionFunction) {
    this.promiseChain = [];
    this.handleError = () => {};

    this.onResolve = this.onResolve.bind(this);
    this.onReject = this.onReject.bind(this);

    executionFunction(this.onResolve, this.onReject);
  }

  then(handleSuccess) {
    this.promiseChain.push(handleSuccess);

    return this;
  }

  catch(handleError) {
    this.handleError = handleError;

    return this;
  }

  onResolve(value) {
    let storedValue = value;

    try {
      this.promiseChain.forEach((nextFunction) => {
         storedValue = nextFunction(storedValue);
      });
    } catch (error) {
      this.promiseChain = [];

      this.onReject(error);
    }
  }

  onReject(error) {
    this.handleError(error);
  }
}

@sudo-suhas
I think we need to pass the initialValue

onResolve(value) {
    try {
      return this.promiseChain.reduce(
        (result, nextFunction) => nextFunction(result)
      ,value);
    } catch (error) {
      this.promiseChain = [];

      this.onReject(error);
    }
  }

Full walkthrough along with video explanation here: https://skilled.dev/course/build-a-javascript-promise