Request payment page

The problem

In this section, we will:

  • Simulate making a 2 second AJAX request to create a payment when someone submits the form.
  • Log console.log("Asking for token with", card) when the request is made.
  • Log console.log("payment complete!"); when the payment is complete.

How to solve the problem

  • Create a appComponent.pay(event) method that is called when the form is submitted.

  • Create a appComponent.paySubmitted$ Subject that emits when pay is called.

  • Create a card$ observable like:

    const card$ = combineCard(this.cardNumber$, this.expiry$, this.cvc$);

    card should publish objects with the cardNumber, expiry, and cvc:

    {
  cardNumber,
  expiry,
  cvc,
};

  • Create a payments$ observable like:

    const payments$ = paymentPromises(this.paySubmitted$, card$);

    payments publishes promises when this.paySubmitted emits. Those promises resolve when the payment is complete.

    The payments observable will not be used in the template so we will need to subscribe to it as follows:

    payments$.subscribe((paymentPromise) => {
  paymentPromise.then(() => {
    console.log('payment complete!');
  });
});

  • Log console.log("Asking for token with", card) when the request is made.

What you need to know

  • Use (event)="method($event)" to listen to an event in the template and call a method with the event.

    <form (submit)="pay($event)"></form>

    Methods are on your component look like:

    class AppComponent {
  pay() {

  }
}

  • Call event.preventDefault() to prevent an submit event from posting to a url.

  • withLatestFrom works like combineLatest, but it only publishes when the source observable emits a value. It publishes an array with the last source value and sibling values.

    source.pipe(withLatestFrom(siblingObservable1, siblingObservable2, ...));

    The following will log the latest random number whenever the page is clicked:

    <div id="clickMe">Click Me</div>
<script src="https://cdnjs.cloudflare.com/ajax/libs/rxjs/7.4.0/rxjs.umd.min.js"></script>
<script type="typescript">
  const { fromEvent, interval } = rxjs;
  const { map, withLatestFrom } = rxjs.operators;

  const randomNumbers = interval(1000).pipe(map(() => Math.random()));

  const clicks = fromEvent(clickMe, "click");

  clicks
    .pipe(withLatestFrom(randomNumbers))
    .subscribe(([clickEvent, number]) => {
      console.log(number);
    });
</script>
  • Use the following to create a Promise that takes 2 seconds to resolve: 
    new Promise((resolve) => {
  setTimeout(() => {
    resolve(1000);
  }, 2000);
});

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, Subject, merge, combineLatest } = rxjs;
  const { map, tap, scan, withLatestFrom } = 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";
    }
  });

  const log = (name) => {
    return tap((value) => console.log(name, value));
  };

  function showOnlyWhenBlurredOnce(error$, blurred$) {
    const errorEvents$ = error$.pipe(
      map((error) => {
        return { type: error ? "invalid" : "valid" };
      })
    );

    const focusEvents$ = blurred$.pipe(
      map((isBlurred) => {
        return { type: isBlurred ? "blurred" : "focused" };
      })
    );

    const events$ = merge(errorEvents$, focusEvents$);

    const eventsToState = scan(
      (previous, event) => {
        switch (event.type) {
          case "valid":
            return { ...previous, isValid: true, showCardError: false };
          case "invalid":
            return {
              ...previous,
              isValid: false,
              showCardError: previous.hasBeenBlurred,
            };
          case "blurred":
            return {
              ...previous,
              hasBeenBlurred: true,
              showCardError: !previous.isValid,
            };
          default:
            return previous;
        }
      },
      {
        hasBeenBlurred: false,
        showCardError: false,
        isValid: false,
      }
    );

    const state$ = events$.pipe(eventsToState);

    return state$.pipe(map((state) => state.showCardError));
  }

  const expiryParts = map((expiry) => {
    if (expiry) {
      return expiry.split("-");
    }
  });

  const validateExpiry = map((expiry) => {
    if (!expiry) {
      return "There is no expiry. Format  MM-YY";
    }
    if (
      expiry.length !== 2 ||
      expiry[0].length !== 2 ||
      expiry[1].length !== 2
    ) {
      return "Expiry must be formatted like MM-YY";
    }
  });

  const validateCVC = map((cvc) => {
    if (!cvc) {
      return "There is no CVC code";
    }
    if (cvc.length !== 3) {
      return "The CVC must be at least 3 numbers";
    }
    if (isNaN(parseInt(cvc))) {
      return "The CVC must be numbers";
    }
  });

  function isCardInvalid(cardError$, expiryError$, cvcError$) {
    return combineLatest([cardError$, expiryError$, cvcError$]).pipe(
      map(([cardError, expiryError, cvcError]) => {
        return !!(cardError || expiryError || cvcError);
      })
    );
  }

  function combineCard(cardNumber$, expiry$, cvc$) {
    return combineLatest([cardNumber$, expiry$, cvc$]).pipe(
      map(([cardNumber, expiry, cvc]) => {
        return {
          cardNumber,
          expiry,
          cvc,
        };
      })
    );
  }

  function paymentPromises(paySubmitted$, card$) {
    return paySubmitted$.pipe(withLatestFrom(card$)).pipe(
      map(([paySubmitted, card]) => {
        console.log("Asking for token with", card);
        return new Promise((resolve) => {
          setTimeout(() => {
            resolve(1000);
          }, 2000);
        });
      })
    );
  }

  @Component({
    selector: 'my-app',
    template: `
      <form (submit)="pay($event)">
        <div class="message" *ngIf="showCardError$ | async">{{ cardError$ | async }}</div>

        <div class="message" *ngIf="showExpiryError$ | async">{{ expiryError$ | async }}</div>

        <div class="message" *ngIf="showCVCError$ | async">{{ cvcError$ | async }}</div>

        <input
          type="text"
          name="cardNumber"
          placeholder="Card Number"
          (input)="userCardNumber$.next($event.target.value)"
          (blur)="userCardNumberBlurred$.next(true)"
          [class.is-error]="showCardError$ | async"
        />

        <input
          type="text"
          name="expiry"
          placeholder="MM-YY"
          (input)="userExpiry$.next($event.target.value)"
          (blur)="userExpiryBlurred$.next(true)"
          [class.is-error]="showExpiryError$ | async"
        />

        <input
          type="text"
          name="cvc"
          placeholder="CVC"
          (input)="userCVC$.next($event.target.value)"
          (blur)="userCVCBlurred$.next(true)"
          [class.is-error]="showCVCError$ | async"
        />

        <button [disabled]="isCardInvalid$ | async">
          PAY
        </button>
      </form>
      UserCardNumber: {{ userCardNumber$ | async }} <br />
      CardNumber: {{ cardNumber$ | async }} <br />
    `
  })
  class AppComponent {
    userCardNumber$ = new BehaviorSubject<string>();
    userCardNumberBlurred$ = new Subject<boolean>();

    userExpiry$ = new BehaviorSubject<[]>();
    userExpiryBlurred$ = new Subject<boolean>();

    userCVC$ = new BehaviorSubject<string>();
    userCVCBlurred$ = new Subject<boolean>();

    paySubmitted$ = new Subject<void>();

    constructor() {
      this.cardNumber$ = this.userCardNumber$
        .pipe(cleanCardNumber)
        .pipe(log("cardNumber"));
      this.cardError$ = this.cardNumber$.pipe(validateCard);
      this.showCardError$ = showOnlyWhenBlurredOnce(this.cardError$, this.userCardNumberBlurred$);

      this.expiry$ = this.userExpiry$.pipe(expiryParts);
      this.expiryError$ = this.expiry$.pipe(validateExpiry);
      this.showExpiryError$ = showOnlyWhenBlurredOnce(this.expiryError$, this.userExpiryBlurred$);

      this.cvc$ = this.userCVC$;
      this.cvcError$ = this.cvc$.pipe(validateCVC);
      this.showCVCError$ = showOnlyWhenBlurredOnce(this.cvcError$, this.userCVCBlurred$);

      this.isCardInvalid$ = isCardInvalid(this.cardError$, this.expiryError$, this.cvcError$);

      const card$ = combineCard(this.cardNumber$, this.expiry$, this.cvc$);

      const payments$ = paymentPromises(this.paySubmitted$, card$);

      payments$.subscribe((paymentPromise) => {
        paymentPromise.then(() => {
          console.log("payment complete!");
        });
      });
    }

    pay(event) {
      event.preventDefault();
      this.paySubmitted$.next();
    }
  }

  // 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>