Javascript

Handling Forms in Svelte

Published Jul 6, 2021

Updated Feb 14, 2023

7 min read

This article was written over 18 months ago and may contain information that is out of date. Some content may be relevant but please refer to the relevant official documentation or available resources for the latest information.

Handling Forms in Svelte

If you're building an app or website, it's very likely that at some point you need to add a form to it.

In this post, we'll dive into how to handle forms in Svelte, starting from a simple approach. Then, we'll start adding complexity to it, and finally, we'll have a reusable solution.

Starting with a simple form

Let's build a sign-in form with two fields: email and password.

We'll begin by creating a new Svelte project (I prefer vite).

npm init @vitejs/app

✔ Project name: · forms-in-svelte
✔ Select a framework: · svelte
✔ Select a variant: · svelte-ts

cd forms-in-svelte
pnpm install //use the package manager you prefer
pnpm run dev

NOTE: At the moment of writing there's a bug with Svelte TypeScript projects. If you get an error, add "type":"module" in your package.json file.

Now that we have our application ready, we'll start by removing the content of App.svelte and create a sign-in form.

We should also delete the Counter component created by default.

<!-- App.svelte -->
<main>
  <form>
    <div>
        <label for="name">Email</label>
        <input
          type="text"
          id="email"
          name="email"
          value=""
        />
    </div>
    <div>
      <label for="name">Password</label>
      <input
        type="password"
        id="password"
        name="password"
        value=""
      />
  </div>
    <button type="submit">Submit</button>
  </form>
</main>

<style>
   * {
      box-sizing: border-box;
    }
    form {
      display: flex;
      flex-direction: column;
      width: 300px;
    }

    form > div{
      display: flex;
      justify-content: space-between;
    }

    form > div + * {
      margin-top: 10px;
    }
</style>

Handling the submit event

Currently, our form does nothing. We need to handle the submit event on the form. To do that, we must add a handler.

To handle a submit event, we need to add to the form element the on:submit handler.

For now, we will only parse the form, and print it in the console.

<!-- App.svelte -->
<script lang="ts">
  function onSubmit(e) {
    const formData = new FormData(e.target);

    const data = {};
    for (let field of formData) {
      const [key, value] = field;
      data[key] = value;
    }
    console.log(data)
  }
</script>

<main>
  <form on:submit|preventDefault={onSubmit}>
   <!-- ... -->
  </form>
</main>
<!-- ... -->

Note that we used the event modifier |preventDefault. This is equivalent to adding the Event preventDefault method in the handler.

Adding validation

Now that our form "works", we can add more features to it. For example, we may want to add some validation when the form is submitted. We will make both inputs required. If the form is invalid, we will print an error in the console. Otherwise, we will print the form data.

<!-- App.svelte -->
<script lang="ts">
  function isFormValid(data: {[fieldName: string]: any}): boolean {
    if(!isRequiredFieldValid(data.email)){
      return false
    }

    if(!isRequiredFieldValid(data.password)){
      return false
    }
    return true
  }

  function isRequiredFieldValid(value){
    return value != null && value !== ""
  }

  function onSubmit(e) {
    const formData = new FormData(e.target);

    const data: any = {};
    for (let field of formData) {
      const [key, value] = field;
      data[key] = value;
    }
    if(isFormValid(data)){
      console.log(data)
    } else {
      console.log("Invalid Form")
    }
  }
</script>
<!-- ... -->

Displaying errors

Now, our form is running a simple validation on submit, but we are missing feedback for the user. It's time to display some errors in case something fails.

<!-- App.svelte -->
<script lang="ts">
  let errors: { [inputName: string]: any } = {};

  function isFormValid(data: { [inputName: string]: any }): boolean {
    return !Object.keys(errors).some((inputName) =>
      Object.keys(errors[inputName]).some(
        (errorName) => errors[inputName][errorName],
      ),
    );
  }

  function validateForm(data: { [inputName: string]: any }):void {
    if (!isRequiredFieldValid(data.email)) {
      errors['email'] = { ...errors['email'], required: true };
    } else {
      errors['email'] = { ...errors['email'], required: false };
    }

    if (!isRequiredFieldValid(data.password)) {
      errors['password'] = { ...errors['password'], required: true };
    } else {
      errors['password'] = { ...errors['password'], required: false };
    }
  }

  function isRequiredFieldValid(value) {
    return value != null && value !== '';
  }

  function onSubmit(e) {
    const formData = new FormData(e.target);

    const data: any = {};
    for (let field of formData) {
      const [key, value] = field;
      data[key] = value;
    }

    validateForm(data);

    if (isFormValid(data)) {
      console.log(data);
    } else {
      console.log('Invalid Form');
    }
  }
</script>

<main>
  <form on:submit|preventDefault={onSubmit}>
    <div>
      <label for="name">Email</label>
      <input type="text" id="email" name="email" value="" />
      {#if errors.email && errors.email.required}
        <p class="error-message">Email is required</p>
      {/if}
    </div>
    <div>
      <label for="name">Password</label>
      <input type="password" id="password" name="password" value="" />
      {#if errors.password && errors.password.required}
        <p class="error-message">Password is required</p>
      {/if}
    </div>
    <button type="submit">Submit</button>
  </form>
</main>

<style>
  /* ... */

  form > div {
    display: flex;
    flex-wrap: wrap;
    justify-content: space-between;
  }

  /* ... */

  .error-message {
    color: tomato;
    flex: 0 0 100%;
    margin: 0 2px;
    font-size: 0.8em;
  }
</style>

First, I created an error object to keep track of each field, and its errors. I created it as an empty object as I expect it to be populated when verification happens.

Three functions will help validation:

isRequiredFieldValid checks if a given value is null, undefined, or an empty string.
validateForm sets errors to true or false for each form input. In this example, we are checking if both required fields are valid.
isFormValidwill check if there's an error in the form.

In the template, error messages are added below each form input, with a message to be displayed if the error is present and true.

Finally, some CSS was added for styling the form.

The result looks something like this:

Preparing for reusability

We have a working form right now, but it would be better if somehow we could make our form reusable.

The pattern will be repeated for each input we add. It would be nice if we could make it configurable, or if we could easily add more errors and validators without repeating ourselves.

Let's move the validators to a new file, and add more information to the response.

// Validators.ts
export interface ValidatorResult {
  [validatorName: string]: {
    error: boolean;
    message?: string;
  };
}

export type ValidatorFn = (value: any) => ValidatorResult;

function required(value: any): ValidatorResult {
  if (value === '' || value == null) {
    return { required: { error: true, message: 'Field is required' } };
  }
  return { required: { error: false } };
}

export const Validators = {
  required,
};

Previously, we had the isRequiredFieldValid method returning just a boolean. Now it returns an object with the error name required, error status, and a message, but can be extended with more information if required.

We now need to make use of this new Validator in our App component.

<!-- App.svelte -->
<script lang="ts">
  import { Validators } from './lib/Validators';
  import type { ValidatorFn, ValidatorResult } from './lib/Validators';

  let errors: { [inputName: string]: ValidatorResult } = {};

  let form: {
    [inputName: string]: {
      validators: ValidatorFn[];
    };
  } = {
    email: {
      validators: [Validators.required],
    },
    password: {
      validators: [Validators.required],
    },
  };

  function isFormValid(): boolean {
    return !Object.values(errors).some((field) =>
      Object.values(field).some((errorObject) => errorObject.error),
    );
  }

  function validateForm(data: { [inputName: string]: any }): void {
    Object.keys(data).forEach((field) => validateField(field, data[field]));
  }

  function validateField(field, value) {
    form[field]?.validators &&
      form[field].validators.forEach((fn) => {
        const error = fn(value);
        errors[field] = { ...errors[field], ...error };
      });
  }

  function onSubmit(e) {
    const formData = new FormData(e.target);

    const data: any = {};
    for (let field of formData) {
      const [key, value] = field;
      data[key] = value;
    }

    validateForm(data);

    if (isFormValid()) {
      console.log(data);
    } else {
      console.log('Invalid Form');
    }
  }
</script>

<main>
  <form on:submit|preventDefault={onSubmit}>
    <div>
      <label for="name">Email</label>
      <input type="text" id="email" name="email" value="" />
      {#if errors?.email?.required?.error}
        <p class="error-message">Email is required</p>
      {/if}
    </div>
    <div>
      <label for="name">Password</label>
      <input type="password" id="password" name="password" value="" />
      {#if errors?.password?.required?.error}
        <p class="error-message">Password is required</p>
      {/if}
    </div>
    <button type="submit">Submit</button>
  </form>
</main>

<!-- ... -->

First, I've created a form object that contains the different input names with a list of the validators that should be checked for each of them.

I added the required validator for both of them.

Then we will run all validators in the form object where the key matches the name of the input element.

The template has been updated too to handle the validator response object.

With this small refactoring, we've preserved our previous behavior, but opened the door to expand our form.

More validators

Let's add another validator to our password input.

We'll check if the password has a minimum length of 6 characters.

We'll start by creating a new validator. The best way is to use a higher-order function to set up the length, and return our validator function from it.

export interface ValidatorResult {
  [validatorName: string]: {[key:string]:any} & {
    error: boolean;
    message?: string;
  };
}

// ...

function minLength(number) {
  return function (value): ValidatorResult {
    if (value == null || value.length < number) {
      return {
        minLength: {
          error: true,
          value: number, 
          message: `Field minimum length is ${number}`,
        },
      };
    }
    return { minLength: { error: false } };
  };
}

export const Validators = {
  required,
  minLength
};

Now, we need to add it to our form configuration object, and handle the error in the template. We are using the error default message.

<!-- App.svelte -->
<script lang="ts">
// ...
  let form: {
    [inputName: string]: {
      validators: ValidatorFn[];
    };
  } = {
    email: {
      validators: [Validators.required],
    },
    password: {
      validators: [Validators.required, Validators.minLength(6)],
    },
  };

 //...
</script>

<main>
  <form on:submit|preventDefault={onSubmit}>
   <!-- ... -->
    <div>
      <label for="name">Password</label>
      <input type="password" id="password" name="password" value="" />
      {#if errors?.password?.required?.error}
        <p class="error-message">Password is required</p>
      {/if}
	  {#if errors?.password?.minLength?.error}
        <p class="error-message">{errors.password.minLength.message}</p>
      {/if}
    </div>
    <button type="submit">Submit</button>
  </form>
</main>

<!-- ... -->

Handling other form events

I want to add another feature to our form. I want to validate each field separately on blur.

We can use an event handler with one of each input element to do it.

<!-- App.svelte -->
<script lang="ts">
  //...

  function onBlur(e){
    validateField(e.target.name, e.target.value)
  }

</script>

<main>
  <form on:submit|preventDefault={onSubmit}>
    <!-- ... -->
      <input type="text" id="email" name="email" value="" on:blur={onBlur} />
    <!-- ... -->
      <input type="password" id="password" name="password" value="" on:blur={onBlur} />
       <!-- ... -->
  </form>
</main>

<!-- ... -->

We just added an on:blur event handler, and onBlur method to take care of everything. Now, everytime an input loses focus it will be validated.

Our form is working as expected. However, I'd like to move it to a new component.

Creating a reusable form component

Let's create a new component Form.svelte, and move most of the form logic into it.

The form configuration should remain in the App component, and be passed into the new Form component.

<!-- Form.svelte -->
<script lang="ts">
  import { setContext } from 'svelte';
  import type { ValidatorFn, ValidatorResult } from './Validators';
  import { createEventDispatcher } from 'svelte';
  import { writable } from 'svelte/store';

  export let form: {
    [inputName: string]: {
      validators: ValidatorFn[];
    };
  } = {};

  let formEl;

  const dispatch = createEventDispatcher();
  let errors = writable({});

  function onBlur(e) {
    validateField(e.target.name, e.target.value);
  }

  function isFormValid(): boolean {
    return !Object.values($errors).some((field) =>
      Object.values(field).some(
        (errorObject: ValidatorResult) => errorObject.error,
      ),
    );
  }

  function validateField(field, value) {
    form[field]?.validators &&
      form[field].validators.forEach((fn) => {
        const error = fn(value);
        errors.update((e) => {
          e[field] = { ...e[field], ...error };
          return e;
        });
      });
  }

  function validateForm(data: { [inputName: string]: any }): void {
    Object.keys(data).forEach((field) => validateField(field, data[field]));
  }

  function onSubmit(e) {
    const formData = new FormData(e.target);

    const data: any = {};
    for (let field of formData) {
      const [key, value] = field;
      data[key] = value;
    }
    validateForm(data);

    return dispatch('submit', { valid: isFormValid(), data });
  }

  export function reset() {
    formEl.reset();
  }

  setContext('form', { errors, onBlur });
</script>

<form on:submit|preventDefault={onSubmit} bind:this={formEl}>
  <slot />
</form>

<style>
  form {
    display: flex;
    flex-direction: column;
    width: 300px;
  }

  :global(form > div) {
    display: flex;
    flex-wrap: wrap;
    justify-content: space-between;
  }

  :global(form > div + *) {
    margin-top: 10px;
  }
</style>

The template is very simple. A form element with a slot.

We are also binding the form element, and the on:submit event.

There's only one input: form, which will be in charge of passing data from the parent component.

The element's binding will be used to expose the native reset method from the form element. And the event binding will be used to perform validations, and emit a new submit event to be handled by the parent component.

One important thing to notice is that, to communicate the slotted elements with the Form component, we will use the Context API. There's one caveat though, context is not reactive. But, we can make it reactive by making its content a store.

Currently, we will only need to pass two things to the slotted content, the onBlur method, and the errors object. Because we expect the error object to be changing, I rewrote it as a writable store. Note that everything that previously used the errors object will have to use this new store.

To keep the parent component simple (the one containing the form), the form content will be wrapped in new components that will make use of the context API to get the data from the Form component.

Because I want always to have a label for any given field, I'll make it part of the Input component, and because I want to add validation on blur, I'll get the onBlur method exposed by the Form component through the context API.

<!-- Input.svelte -->
<script lang="ts">
  import { getContext } from 'svelte';
  export let type = 'text';
  export let label;
  export let name;
  const { onBlur } = getContext('form');
</script>

<label for={name}>{label}</label>
<input {name} {type} on:blur={onBlur} />

We are closer to getting the same behavior as before, but we are missing the error components. We can wrap all that functionality in a single component, and get the error information through the context API.

<!-- Error.svelte -->
  import { getContext } from 'svelte';
  const { errors } = getContext('form');
  export let message = null;
  export let fieldName;
  export let errorKey;
</script>

{#if $errors?.[fieldName]?.[errorKey]?.error}
  <p class="error-message">{message || $errors[fieldName][errorKey].message}</p>
{/if}

<style>
  .error-message {
    color: tomato;
    flex: 0 0 100%;
    margin: 0 2px;
    font-size: 0.8em;
  }
</style>

We are now reading the value from the errors store to decide if the message should be shown or not.

We are also using a default message from the validator in case no message is provided.

Now that all the pieces are ready, we can update our App component.

<!-- App.svelte -->
<script lang="ts">
  import { Validators } from './lib/Validators';
  import Form from './lib/Form.svelte';
  import Input from './lib/Input.svelte';
  import Error from './lib/Error.svelte';

  let formEl;
  let form = {
    email: {
      validators: [Validators.required],
    },
    password: {
      validators: [Validators.required, Validators.minLength(6)],
    },
  };

  function onSubmit(e) {
    if (e?.detail?.valid) {
      console.log(e.detail.data);
      setTimeout(() => formEl.reset(), 1000)
    } else {
      console.log('Invalid Form');
    }
  }
</script>

<main>
  <Form {form} on:submit={onSubmit} bind:this={formEl}>
    <div>
      <Input label="Email" name="email" />
      <Error
        fieldName="email"
        errorKey="required"
        message="Email is required"
      />
    </div>
    <div>
      <Input label="Password" name="password" />
      <Error
        fieldName="password"
        errorKey="required"
        message="Password is required"
      />
      <Error fieldName="password" errorKey="minLength" />
    </div>
    <button type="submit">Submit</button>
  </Form>
</main>

<style>
  * {
    box-sizing: border-box;
  }
</style>

Our app component now only needs to set up the validators, handle the submit event, and can reset the form if needed.

Extending the form component

Our form component is now exposing just a few things emitted on the submit event, or through the context API, for the slotted components.

Similar to what we've done with the input field, we must extend the functionality for select, radio buttons, checkboxes, or any other form control that we want.

For example, this is how a select component may look like.

<!-- Select.svelte -->
<script lang="ts">
  import { getContext } from 'svelte';
  export let label;
  export let name;
  const { onBlur } = getContext('form');
</script>

<label for={name}>{label}</label>
<select {name} on:blur={onBlur}>
  <slot />
</select>

And this is how it could be used:

<!-- App.svelte -->
<script lang="ts">
  import { Validators } from './lib/Validators';
  import Form from './lib/Form.svelte';
  import Input from './lib/Input.svelte';
  import Error from './lib/Error.svelte';
  import Select from './lib/Select.svelte';

  let form = {
    name: {
      validators: [Validators.required],
    },
    food: {
      validators: [Validators.required],
    },
  };

  let formEl;

  function onSubmit(e) {
    if (e?.detail?.valid) {
      console.log(e.detail.data);
      setTimeout(() => formEl.reset(), 1000)
    } else {
      console.log('Invalid Form');
    }
  }
</script>

<main>
  <Form {form} on:submit={onSubmit} bind:this={formEl}>
    <div>
      <Input label="Name" name="name" />
      <Error
        fieldName="name"
        errorKey="required"
        message="Name is required"
      />
    </div>
    <div>
      <Select label="Favorite food" name="food">
        <option value="chocolate">Chocolate</option>
        <option value="pizza">Pizza</option>
      </Select>
    </div>
    <button type="submit">Submit</button>
  </Form>
</main>
<!-- ... -->

Available Libraries

There are plenty of available libraries for handling forms in Svelte. You can check some of them in this list.

Final thoughts

I hope this step-by-step guide to handling forms helps you find your own solution to handling them, or gives you a better understanding of how other libraries might be working.

This Dot is a consultancy dedicated to guiding companies through their modernization and digital transformation journeys. Specializing in replatforming, modernizing, and launching new initiatives, we stand out by taking true ownership of your engineering projects.

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About the author(s)

Ignacio Falk
I love to learn new things and share what I know. Mentor, Writer, Speaker Member of the local community
@flakolefluk @flakolefluk

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HTMLJavaScript

Introduction to Zod for Data Validation

As web developers, we're often working with data from external sources like APIs we don't control or user inputs submitted to our backends. We can't always rely on this data to take the form we expect, and we can encounter unexpected errors when it deviates from expectations. But with the Zod library, we can define what our data ought to look like and parse the incoming data against those defined schemas. This lets us work with that data confidently, or to quickly throw an error when it isn't correct. Why use Zod? TypeScript is great for letting us define the shape of our data in our code. It helps us write more correct code the first time around by warning us if we are doing something we shouldn't. But TypeScript can't do everything for us. For example, we can define a variable as a string or a number, but we can't say "a string that starts with user_id_ and is 20 characters long" or "an integer between 1 and 5". There are limits to how much TypeScript can narrow down our data for us. Also, TypeScript is a tool for us developers. When we compile our code, our types are not available to the vanilla JavaScript. JavaScript can't validate that the data we actually use in our code matches what we thought we'd get when we wrote our TypeScript types unless you're willing to manually write code to perform those checks. This is where we can reach for a tool like Zod. With Zod, we can write data schemas. These schemas, in the simplest scenarios, look very much like TypeScript types. But we can do more with Zod than we can with TypeScript alone. Zod schemas let us create additional rules for data parsing and validation. A 20-character string that starts with user_id_? It's z.string().startsWith('user_id_').length(20). An integer between 1 and 5 inclusive? It's z.number().int().gte(1).lte(5). Zod's primitives give us many extra functions to be more specific about *exactly* what data we expect. Unlike TypeScript, Zod schemas aren't removed on compilation to JavaScript—we still have access to them! If our app receives some data, we can verify that it matches the expected shape by passing it to your Zod schema's parse function. You'll either get back your data in exactly the shape you defined in your schema, or Zod will give you an error to tell you what was wrong. Zod schemas aren't a replacement for TypeScript; rather, they are an excellent complement. Once we've defined our Zod schema, it's simple to derive a TypeScript type from it and to use that type as we normally would. But when we really need to be sure our data conforms to the schema, we can always parse the data with our schema for that extra confidence. Defining Data Schemas Zod schemas are the variables that define our expectations for the shape of our data, validate those expectations, and transform the data if necessary to match our desired shape. It's easy to start with simple schemas, and to add complexity as required. Zod provides different functions that represent data structures and related validation options, which can be combined to create larger schemas. In many cases, you'll probably be building a schema for a data object with properties of some primitive type. For example, here's a schema that would validate a JavaScript object representing an order for a pizza: ` Zod provides a number of primitives for defining schemas that line up with JavaScript primitives: string, number, bigint, boolean, date, symbol, undefined, and null. It also includes primitives void, any, unknown, and never for additional typing information. In addition to basic primitives, Zod can define object, array, and other native data structure schemas, as well as schemas for data structures not natively part of JavaScript like tuple and enum. The documentation contains considerable detail on the available data structures and how to use them. Parsing and Validating Data with Schemas With Zod schemas, you're not only telling your program what data should look like; you're also creating the tools to easily verify that the incoming data matches the schema definitions. This is where Zod really shines, as it greatly simplifies the process of validating data like user inputs or third party API responses. Let's say you're writing a website form to register new users. At a minimum, you'll need to make sure the new user's email address is a valid email address. For a password, we'll ask for something at least 8 characters long and including one letter, one number, and one special character. (Yes, this is not really the best way to write strong passwords; but for the sake of showing off how Zod works, we're going with it.) We'll also ask the user to confirm their password by typing it twice. First, let's create a Zod schema to model these inputs: ` So far, this schema is pretty basic. It's only making sure that whatever the user types as an email is an email, and it's checking that the password is at least 8 characters long. But it is *not* checking if password and confirmPassword match, nor checking for the complexity requirements. Let's enhance our schema to fix that! ` By adding refine with a custom validation function, we have been able to verify that the passwords match. If they don't, parsing will give us an error to let us know that the data was invalid. We can also chain refine functions to add checks for our password complexity rules: ` Here we've chained multiple refine functions. You could alternatively use superRefine, which gives you even more fine grained control. Now that we've built out our schema and added refinements for extra validation, we can parse some user inputs. Let's see two test cases: one that's bound to fail, and one that will succeed. ` There are two main ways we can use our schema to validate our data: parse and safeParse. The main difference is that parse will throw an error if validation fails, while safeParse will return an object with a success property of either true or false, and either a data property with your parsed data or an error property with the details of a ZodError explaining why the parsing failed. In the case of our example data, userInput2 will parse just fine and return the data for you to use. But userInput1 will create a ZodError listing all of the ways it has failed validation. ` ` We can use these error messages to communicate to the user how they need to fix their form inputs if validation fails. Each error in the list describes the validation failure and gives us a human readable message to go with it. You'll notice that the validation errors for checking for a valid email and for checking password length have a lot of details, but we've got three items at the end of the error list that don't really tell us anything useful: just a custom error of Invalid input. The first is from our refine checking if the passwords match, and the second two are from our refine functions checking for password complexity (numbers and special characters). Let's modify our refine functions so that these errors are useful! We'll add our own error parameters to customize the message we get back and the path to the data that failed validation. ` Now, our error messages from failures in refine are informative! You can figure out which form fields aren't validating from the path, and then display the messages next to form fields to let the user know how to remedy the error. ` By giving our refine checks a custom path and message, we can make better use of the returned errors. In this case, we can highlight specific problem form fields for the user and give them the message about what is wrong. Integrating with TypeScript Integrating Zod with TypeScript is very easy. Using z.infer<typeof YourSchema> will allow you to avoid writing extra TypeScript types that merely reflect the intent of your Zod schemas. You can create a type from any Zod schema like so: ` Using a TypeScript type derived from a Zod schema does *not* give you any extra level of data validation at the type level beyond what TypeScript is capable of. If you create a type from z.string.min(3).max(20), the TypeScript type will still just be string. And when compiled to JavaScript, even that will be gone! That's why you still need to use parse/safeParse on incoming data to validate it before proceeding as if it really does match your requirements. A common pattern with inferring types from Zod schemas is to use the same name for both. Because the schema is a variable, there's no name conflict if the type uses the same name. However, I find that this can lead to confusing situations when trying to import one or the other—my personal preference is to name the Zod schema with Schema at the end to make it clear which is which. Conclusion Zod is an excellent tool for easily and confidently asserting that the data you're working with is exactly the sort of data you were expecting. It gives us the ability to assert at runtime that we've got what we wanted, and allows us to then craft strategies to handle what happens if that data is wrong. Combined with the ability to infer TypeScript types from Zod schemas, it lets us write and run more reliable code with greater confidence....

Nov 15, 2024

7 mins

JavaScriptZod

Overview of the New Signal APIs in Angular

Overview of the New Signal APIs in Angular Google's Minko Gechev and Jeremy Elbourn announced many exciting things at NG Conf 2024. Among them is the addition of several new signal-based APIs. They are already in developer preview, so we can play around with them. Let's dig into it, starting with signal-based inputs and the new matching outputs API. Signal Based Inputs Discussions about signal-based inputs have been taking place in the Angular community for some time now, and they are finally here. Until now, you used the @Input() decorator to define inputs. This is what you'd have to write in your component to declare an optional and a required input: ` With the new signal-based inputs, you can write much less boilerplate code. Here is how you can define the same inputs using the new syntax: ` It's not only less boilerplate, but because the values are signals, you can also use them directly in computed signals and effects. That, effectively, means you get to avoid computing combined values in ngOnChanges or using setters for your inputs to be able to compute derived values. In addition, input signals are read-only. The New Output I intentionally avoid calling them signal-based outputs because they are not. They still work the same way as the old outputs. The Angular team has just introduced a new output API that is more consistent with the latest inputs API and allows you to write less boilerplate, similar to the new input API. Here is how you would define an output until now: ` Here is how you can define the same output using the new syntax: ` The thing I like about the new output API is that sometimes it happens to me that I forget to instantiate the EventEmitter because I do this instead: ` You won't forget to instantiate the output with the new syntax because the output function does it for you. Signal Queries I am sure most readers know the @ViewChild, @ViewChildren, @ContentChild, and @ContentChildren decorators very well and have experienced the pain of triggering the infamous ExpressionChangedAfterItHasBeenCheckedError or having the values unavailable when needed. Here is a refresher on how you would use these decorators until now: ` With the new signal queries, similar to the new input API, the values are signals, and you can use them directly in computed signals and effects. You can define the same queries using the new syntax: ` Jeremy Elbourn mentioned that the new signal queries have better type inference and are more consistent with the new input and output APIs. He also showcased a brand new feature not available with the old queries. You can now define a query as required, and the Angular compiler will throw an error if the query has no result, guaranteeing that the value won't be undefined. Here is how you can define a required query: ` Model Inputs Jeremy and Minko announced the last new feature is the model inputs. The name is vague, but the feature is cool—it simplifies the definition of two-way bindings. Until now, to achieve two-way binding, you would have to define an input and an output following a given naming convention. @Input and @Output had to be defined with the same name (followed by "Change" in the case of the output). Then, you could use the template's [()] syntax. ` ` That way, you could keep the value in sync between the parent and the child component. With the new model inputs, you can define a two-way binding with a single line of code. Here is how you can define the same two-way binding using the new syntax: ` The html template stays the same: ` The model function returns a writable signal that can be updated directly. The value will be propagated back to any two-way bindings. Conclusion The new signal-based APIs are a great addition to Angular. They allow you to write less boilerplate code and make your components more reactive. The new APIs are already in developer preview, so you can start playing around with them today. I look forward to seeing how the community will adopt these new features and what other exciting things the Angular team has in store for us, such as zoneless apps by default....

Apr 3, 2024

3 mins

AngularJavaScript

Building a Stripe App: A Step-by-Step Guide to QR Code Generation

Building a Stripe App: A Step-by-Step Guide to QR Code Generation Why Build a Stripe App? I recently participated in an audio space with the Stripe team, and something they said really stuck with me: the Stripe app store is a growing area that isn't overly saturated yet. There's a lot of potential for new apps, and companies can use this opportunity to grow. I work at a company called This Dot Labs, and we've created several Stripe apps and even own one. After looking at the data, I can confirm that the Stripe team was right! Creating a QR Code Generator App For this tutorial, we'll build a QR code app that can take a URL and generate a code for it. This is a good use case to help you understand the ins and outs of Stripe's developer tools. Why QR Codes? QR codes are useful tools that have become common in e-commerce, restaurants, and other industries. While Stripe already has a QR code tool, we'll make our own to familiarize ourselves with their syntax and problem-solving approaches. Project Structure Before we dive into the implementation, let's look at the structure of our Stripe App QR Code project: * .vscode: Contains settings for Visual Studio Code * source/views: Holds the main application views * .gitignore: Specifies files to ignore in version control * stripe-app.json: Defines the Stripe app configuration * ui-extensions.d.ts: TypeScript declaration file for UI extensions * .build: this is where the built Stripe app gets placed. Step-by-Step Implementation 1\. Install Stripe Locally First, you need to install Stripe on your local machine. The documentation provides great instructions for this: * For Mac users: Use Brew to install * For Windows users: Download the package and add it to your environment variables You can find the details here in the stripe docs to install the Stripe CLI https://docs.stripe.com/stripe-cli When using Windows, you must do stripe login from Powershell, NOT from Git bash or any other tool. After the server is up, then you can continue using git bash for everything else. After stripe login, you need to enter stripe apps start. Once you do that, the server is up and running and you can go back to using git bash or any other tool. 2\. Install Dependencies We'll be using an extra package for QR code generation. Install it using npm: ` 3\. Set Up the Main Component Let's look at the home.tsx file, where we'll use Stripe's UI components: ` These components are similar to other UI libraries like Bootstrap or Tailwind CSS. 4\. Create the UI Structure Our app will have: * An input field for the URL * Validation using a regex pattern * Error handling for invalid URLs * QR code generation and display Here is the Home.tsx file that is located in the src/views folder ` * ContextView` is at the top level of the app where we see the Title and the link to the Stripe Docs that we placed in our Context View. * Box is how you use Divs. * Banners can be used to show notification errors or any other item you wish to display. * Textfields are input fields. * Everything else is pretty self-explanatory. 5\. Handle Content Security Policy One problem I personally ran into was when I tried to redirect users, the Stripe policies would block it since I did not express that I knew what it was doing. I had to go into the stripe-app.json file and mention the specific security policies. For this particular exercise, I kept these as null. This is my stripe-app.json file. ` 6\. Configure App Views As you can see here, the stripe-app.json file shows the views for each file I have. The Home.tsx file and the Invoice.tsx are also included This is our way of saying that for each view we have, show the app functionality on that page. Our stripe-app.json file will show it but also, the manifest.js file in our .build folder will also show the same. Any view that doesn't have a file will not show the application's functionality. So, if I were to go to transactions, the app would not show the same logic as the home or invoices page. By following these steps, you'll have a fully functional QR code generator app for Stripe. This is just a simple example, but the potential for Stripe apps is massive, especially for businesses serving e-commerce customers. If you need help or get stuck, don't hesitate to reach out, danny.thompson@thisdot.co. The Stripe team is also very active in answering questions, so leverage them as a resource. Happy coding!...

Dec 18, 2024

4 mins

stripe

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Handling Forms in Svelte

Handling Forms in Svelte

Starting with a simple form

Handling the submit event

Adding validation

Displaying errors

Preparing for reusability

More validators

Handling other form events

Creating a reusable form component

Extending the form component

Available Libraries

Final thoughts

Ignacio Falk

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