---
title: Bitovi Academy - Card error
description: Map one observable to another observable again!
---

- ![AI implementation](https://www.bitovi.com/hubfs/AIConsultingIcon.svg)
  
  [AI implementation](https://www.bitovi.com/services/ai-consulting?hsLang=en-us)
- ![Systems engineering](https://www.bitovi.com/hubfs/icon%20-%20backend.svg)
  
  [Systems engineering](https://www.bitovi.com/services/systems-engineering-consulting?hsLang=en-us)
- ![Project management](https://www.bitovi.com/hubfs/icon%20-%20PM.svg)
  
  [Project management](https://www.bitovi.com/services/agile-project-management-consulting?hsLang=en-us)
- ![Product design](https://www.bitovi.com/hubfs/icon%20-%20design.svg)
  
  [Product design](https://www.bitovi.com/services/product-design-consulting?hsLang=en-us)
- ![Frontend development](https://www.bitovi.com/hubfs/icon%20-%20frontend.svg)
  
  [Frontend development](https://www.bitovi.com/services/frontend-development-consulting?hsLang=en-us)
- [View more
  
  →
  
  ](https://www.bitovi.com/digital-consulting-services?hsLang=en-us)

We're Experts in...

- [JavaScript](https://www.bitovi.com/services/frontend/javascript-consulting?hsLang=en-us)
- [AI training](https://www.bitovi.com/ai-training-for-software-engineers?hsLang=en-us)
- [Angular](https://www.bitovi.com/services/frontend/angular-consulting?hsLang=en-us)
- [Design Systems](https://www.bitovi.com/services/axure-figma-migration?hsLang=en-us)
- [React](https://www.bitovi.com/services/frontend/react-consulting?hsLang=en-us)
- [Temporal](https://www.bitovi.com/services/backend/temporal-consulting?hsLang=en-us)
- [React Native](https://www.bitovi.com/services/frontend/react-consulting/react-native?hsLang=en-us)
- [Node.js](https://www.bitovi.com/services/backend/nodejs-consulting-1?hsLang=en-us)

Showcase

![Yum! Brands](https://www.bitovi.com/hubfs/yum-showcase-link-1.png)

[View case study](https://www.bitovi.com/en/bitovi-yum-case-study?hsLang=en-us)

More Projects

- [![Levi's](https://www.bitovi.com/hubfs/levis.svg)](https://www.bitovi.com/web-application-consulting-work/levis-ecommerce-responsive-redesign?hsLang=en-us)
- [![Christie's International Real Estate](https://www.bitovi.com/hubfs/christies.svg)](https://design.bitovi.com/christies)
- [![BAFS](https://www.bitovi.com/hubfs/bafs.svg)](https://www.bitovi.com/ux-design-consulting/ux-case-studies/bafs-ppp?hsLang=en-us)
- [View more
  
  →
  
  ](https://www.bitovi.com/our-software-consulting-work?hsLang=en-us)

Open Source Tools

We build powerful tools and open source them to support the community.

[See what we've built →](https://www.bitovi.com/open-source?hsLang=en-us)

- [![Blog](https://www.bitovi.com/hubfs/icon%20-%20blog.svg)
  
  BlogWe post about perfecting software delivery
  
  ](https://bitovi.com/blog)
- [![Partnerships](https://www.bitovi.com/hubfs/Handshake-1.svg)
  
  PartnershipsLearn about Bitovi's technology partners
  
  ](https://www.bitovi.com/partnerships?hsLang=en-us)
- [![Academy](https://www.bitovi.com/hubfs/limbo/icons/icon-academy.svg)
  
  AcademyFree courses to build delivery skills
  
  ](https://www.bitovi.com/academy/?hsLang=en-us)
- [![Open source tools](https://www.bitovi.com/hubfs/icon%20-%20open%20source.svg)
  
  Open source toolsUse our tools or contribute to our open source mission.
  
  ](https://www.bitovi.com/open-source?hsLang=en-us)

Let's Connect

- [![Discord](https://www.bitovi.com/hubfs/DiscordLogo.svg)
  
  Discord
  
  ](https://discord.gg/J7ejFsZnJ4)
- [![LinkedIn](https://www.bitovi.com/hubfs/LinkedinLogo.svg)
  
  LinkedIn
  
  ](https://www.linkedin.com/company/bitovi/)
- [![GitHub](https://www.bitovi.com/hubfs/GithubLogo.svg)
  
  GitHub
  
  ](https://github.com/bitovi/)

![Eggbot](https://www.bitovi.com/hubfs/build_assets/bitovi-limbo-cms-react/338/js_client_assets/assets/eggbot-LTGhdSGL.png)

Name *

Work Email *

Phone

What's your project?

Send

### Contact Us

(312) 620-0386contact@bitovi.com

- [ Advanced JavaScript ](https://www.bitovi.com/academy/learn-advanced-javascript.html?hsLang=en-us)
- [ DOM and jQuery ](https://www.bitovi.com/academy/learn-dom-jquery.html?hsLang=en-us)
- [ Debug JavaScript ](https://www.bitovi.com/academy/learn-to-debug-javascript.html?hsLang=en-us)
- [ Learn TypeScript ](https://www.bitovi.com/academy/learn-typescript.html?hsLang=en-us)
- [ Learn React Native ](https://www.bitovi.com/academy/learn-react-native.html?hsLang=en-us)
- [ Learn Web Components ](https://www.bitovi.com/academy/learn-web-components.html?hsLang=en-us)
- [ Agile Program Management With Jira ](https://www.bitovi.com/academy/learn-agile-program-management-with-jira.html?hsLang=en-us)
- [ Learn RxJS ](https://www.bitovi.com/academy/learn-rxjs.html?hsLang=en-us) 
    - [ Basics ](https://www.bitovi.com/academy/learn-rxjs/basics.html?hsLang=en-us)
    - [ RxJS in Angular ](https://www.bitovi.com/academy/learn-rxjs/angular.html?hsLang=en-us)
    - [ Clean card number ](https://www.bitovi.com/academy/learn-rxjs/clean-card-number.html?hsLang=en-us)
    - [ Card error ](https://www.bitovi.com/academy/learn-rxjs/card-error.html?hsLang=en-us)
    - [ Debugging ](https://www.bitovi.com/academy/learn-rxjs/debugging.html?hsLang=en-us)
    - [ Error on blur ](https://www.bitovi.com/academy/learn-rxjs/error-on-blur.html?hsLang=en-us)
    - [ Expiry ](https://www.bitovi.com/academy/learn-rxjs/expiry.html?hsLang=en-us)
    - [ CVC ](https://www.bitovi.com/academy/learn-rxjs/cvc.html?hsLang=en-us)
    - [ Disable pay button ](https://www.bitovi.com/academy/learn-rxjs/disable-pay-button.html?hsLang=en-us)
    - [ Request payment ](https://www.bitovi.com/academy/learn-rxjs/request-payment.html?hsLang=en-us)
    - [ Show paying ](https://www.bitovi.com/academy/learn-rxjs/show-paying.html?hsLang=en-us)
    - [ Disable while pending ](https://www.bitovi.com/academy/learn-rxjs/disable-while-pending.html?hsLang=en-us)
- [ Giving a Training ](https://www.bitovi.com/academy/training.html?hsLang=en-us)
- [ Learn Technology Consulting ](https://www.bitovi.com/academy/learn-technology-consulting.html?hsLang=en-us)
- [ Learn React ](https://www.bitovi.com/academy/learn-react.html?hsLang=en-us)
- [ Learn NgRx ](https://www.bitovi.com/academy/learn-ngrx.html?hsLang=en-us)
- [ Learn Graphql ](https://www.bitovi.com/academy/learn-graphql.html?hsLang=en-us)
- [ Learn Docker ](https://www.bitovi.com/academy/learn-docker.html?hsLang=en-us)
- [ Learn CanJS ](https://www.bitovi.com/academy/learn-canjs.html?hsLang=en-us)
- [ Learn Angular ](https://www.bitovi.com/academy/learn-angular.html?hsLang=en-us)
- [ Advanced TypeScript ](https://www.bitovi.com/academy/advanced-typescript.html?hsLang=en-us)

[View More Courses](https://www.bitovi.com/academy/#courses) [ ]

# Card error `page`

Map one observable to another observable again!

## Video

Who has time to read? This video covers the content on this page. Watch fullscreen.

## The problem

In this section, we will:

- Display an error message if the user has not entered a card or the card number is not 16 digits.

## How to solve this problem

- Create a `cardError$` observable that represents this error.
- `cardError$` should emit: 
    - *"There is no card"* if the `cardNumber` is falsy.
    - *"There should be 16 characters in a card"* if the length of `cardNumber` is not 16 digits.
- `cardError$` should be displayed within the `<div class="message">` element.

## What you need to know

You know everything you need to know already.

> HINT: Create a `validateCard` operator with `map`.

## The solution

Click to see the solution

```
<script src="https://cdnjs.cloudflare.com/ajax/libs/rxjs/7.4.0/rxjs.umd.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/core-js/3.19.0/core.js"></script>
<script src="https://unpkg.com/@angular/core@12.2.16/bundles/core.umd.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/zone.js/0.11.4/zone.min.js"></script>
<script src="https://unpkg.com/@angular/common@12.2.16/bundles/common.umd.js"></script>
<script src="https://unpkg.com/@angular/compiler@12.2.16/bundles/compiler.umd.js"></script>
<script src="https://unpkg.com/@angular/platform-browser@12.2.16/bundles/platform-browser.umd.js"></script>
<script src="https://unpkg.com/@angular/platform-browser-dynamic@12.2.16/bundles/platform-browser-dynamic.umd.js"></script>
<my-app></my-app>
<script type="typescript">
  // app.js
  const { Component, VERSION } = ng.core;
  const { BehaviorSubject } = rxjs;
  const { map, tap } = rxjs.operators;

  const cleanCardNumber = map((card) => {
    if (card) {
      return card.replace(/[\s-]/g, "");
    }
  });

  const validateCard = map((card) => {
    if (!card) {
      return "There is no card";
    }
    if (card.length !== 16) {
      return "There should be 16 characters in a card";
    }
  });

  @Component({
    selector: 'my-app',
    template: `
      <form>
        <div class="message">{{ cardError$ | async }}</div>

        <input
          type="text"
          name="cardNumber"
          placeholder="Card Number"
          (input)="userCardNumber$.next($event.target.value)"
        />

        <input type="text" name="expiry" placeholder="MM-YY" />

        <input type="text" name="cvc" placeholder="CVC" />

        <button>
          PAY
        </button>
      </form>
      UserCardNumber: {{ userCardNumber$ | async }} <br />
      CardNumber: {{ cardNumber$ | async }} <br />
    `
  })
  class AppComponent {
    userCardNumber$ = new BehaviorSubject<string>();

    constructor() {
      this.cardNumber$ = this.userCardNumber$.pipe(cleanCardNumber);
      this.cardError$ = this.cardNumber$.pipe(validateCard);
    }
  }

  // main.js
  const { BrowserModule } = ng.platformBrowser;
  const { NgModule } = ng.core;
  const { CommonModule } = ng.common;

  @NgModule({
    imports: [
      BrowserModule,
      CommonModule,
    ],
    declarations: [AppComponent],
    bootstrap: [AppComponent],
    providers: []
  })
  class AppModule {}

  const { platformBrowserDynamic } = ng.platformBrowserDynamic;

  platformBrowserDynamic()
    .bootstrapModule(AppModule)
    .catch(err => console.error(err));
</script>
<style>
  @import url('https://fonts.googleapis.com/css?family=Raleway:400,500');
  body {
    background-color: rgba(8, 211, 67, 0.3);
    padding: 2%;
    font-family: 'Raleway', sans-serif;
    font-size: 1em;
  }
  input {
    display: block;
    width: 100%;
    box-sizing: border-box;
    font-size: 1em;
    font-family: 'Raleway', sans-serif;
    font-weight: 500;
    padding: 12px;
    border: 1px solid #ccc;
    outline-color: white;
    transition: background-color 0.5s ease;
    transition: outline-color 0.5s ease;
  }
  input[name='cardNumber'] {
    border-bottom: 0;
  }
  input[name='expiry'],
  input[name='cvc'] {
    width: 50%;
  }
  input[name='expiry'] {
    float: left;
    border-right: 0;
  }
  input::placeholder {
    color: #999;
    font-weight: 400;
  }
  input:focus {
    background-color: rgba(130, 245, 249, 0.1);
    outline-color: #82f5f9;
  }
  input.is-error {
    background-color: rgba(250, 55, 55, 0.1);
  }
  input.is-error:focus {
    outline-color: #ffbdbd;
  }
  button {
    font-size: 1em;
    font-family: 'Raleway', sans-serif;
    background-color: #08d343;
    border: 0;
    box-shadow: 0px 1px 3px 1px rgba(51, 51, 51, 0.16);
    color: white;
    font-weight: 500;
    letter-spacing: 1px;
    margin-top: 30px;
    padding: 12px;
    text-transform: uppercase;
    width: 100%;
  }
  button:disabled {
    opacity: 0.4;
    background-color: #999999;
  }
  form {
    background-color: white;
    box-shadow: 0px 17px 22px 1px rgba(51, 51, 51, 0.16);
    padding: 40px;
    margin: 0 auto;
    max-width: 500px;
  }
  .message {
    margin-bottom: 20px;
    color: #fa3737;
  }
</style>

```

###### On this page...

###### Get help

If you need [help](https://discord.gg/J7ejFsZnJ4) with an exercise, please reach out to us on [Discord](https://discord.gg/J7ejFsZnJ4)

If you find a bug, please [create an issue](https://github.com/bitovi/academy/issues/new) or email [contact@bitovi.com](mailto:contact@bitovi.com?Subject=Training%20Suggestion)

## Join the Bitovi Newsletter

 Do you want to receive updates about new Bitovi Academy courses, Bitovi open source projects, and dev community news? If so, please provide your email. We won’t spam you or give it away for any reason!  
*By providing your email you agree to receive communications from Bitovi*

![](https://bitovi.github.io/academy/static/img/close.svg)

```json
{
     "@context": "http://schema.org",
     "@type": "Organization",
     "mainEntityOfPage":{
          "@type":"WebPage",
          "@id":"https://www.bitovi.com/academy/learn-rxjs/card-error.html",
          "description": "Map one observable to another observable again! 
"
     },
     "url": "http://bitovi.com",
     "logo": "https://www.bitovi.com/hubfs/bitovi-logo-23-1.svg",
     "image": "https://www.bitovi.com/hubfs/bitovi-logo-x2.png",
     "name": "Bitovi Web App Consulting",
     "alternateName": "Bitovi",
      "naics": "541511",
      "description": "Bitovi is a UX, UI design and front-end JavaScript development consulting company",
     "address": {
          "@type": "PostalAddress",
          "streetAddress": "1134 Pine Tree Lane ",
          "addressLocality": "Libertyville",
          "addressRegion": "IL",
          "addressCountry": "United States",
          "postalCode": "60048"
     },
     "areaServed": {
          "@type": "GeoCircle",
          "geoMidpoint": {
               "@type": "GeoCoordinates",
               "latitude": "41.8781",
               "longitude": "87.6298"
          },
          "geoRadius": "5000 km"
     },
     "telephone": "312-620-0386",
     "email": "contact@bitovi.com",
     "sameAs": [
          "https://www.facebook.com/BitoviLLC/",
          "https://twitter.com/bitovi",
          "https://www.linkedin.com/company/bitovi"
     ]
}
```