General

Building Your First App Using Fresh Framework

Published Oct 7, 2022

Updated Feb 13, 2023

6 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This article was written over 18 months ago and may contain information that is out of date.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.

The Fresh framework is the new kid on the block among frontend meta-frameworks. Just like other React meta-frameworks such as Next.js, Fresh allows you to build pages using React syntax. Unlike Next.js, though, Fresh uses Preact, a fast React alternative with the same API, instead of React. Fresh also stands out by using Deno instead of Node, a fast runtime that supports JavaScript, TypeScript, and WebAssembly.

In this blog post, I will guide you through writing a full-stack app using the Fresh framework.

The App Architecture

The app will be a currency converter that will let you input an amount, the currency to convert from, and the currency to convert to and will show you the converted amount on the screen. It will do this through a combination of client-side rendered code, and server-rendered code.

The app will utilize most of Fresh's framework features for building full-stack apps. As seen in the above picture, it will have a small interactive "island" which is basically a form with the input amount, the source currency, and the target currency.

Once you hit the "Convert" button, the Convert button will change its label (this is the client-side "interactive" part) and trigger form submission to the /convert?amount=X&from=Y&to&Z route that will, before rendering the page, execute a request towards an external currency exchange API, fetch the exchange rate, and display the converted amount in the returned page.

For the server-side part, we will utilize Deno Deploy, the recommended way of deploying Fresh apps to production. The external currency exchange will be provided by CurrencyScoop, which offers a nice API with a generous free tier.

Finally, we will use Tailwind for decorating our page, since Fresh comes with first-class support for Tailwind, as you'll see further down when we scaffold the app.

Getting API Key from CurrencyScoop

Although CurrencyScoop has a free tier that allows you to fetch their currency exchange rates, you'll need to register first and obtain an API key in order to authenticate and use the service. The API key is located on the accounts page as shown in the screenshot below. Copy it and save it for later.

Scaffolding the Fresh app

To scaffold the Fresh app, install Deno if you still haven't, and then execute the following command:

deno run -A -r https://fresh.deno.dev fresh-currency-converter

This will start generating the project, and ask you a couple of questions along the way:

➜  Temp deno run -A -r https://fresh.deno.dev fresh-currency-converter
Download https://fresh.deno.dev/
Download https://deno.land/x/fresh@1.1.1/init.ts
...
Download https://deno.land/std@0.140.0/path/_util.ts

  🍋 Fresh: the next-gen web framework.

Let's set up your new Fresh project.

Fresh has built-in support for styling using Tailwind CSS. Do you want to use this? [y/N] y
Do you use VS Code? [y/N] n
The manifest has been generated for 3 routes and 1 islands.

As you can see, Fresh has first-class support for Tailwind, so we've enabled that. I did not choose the VS Code option myself, but if you use VS Code, then you can use the Deno extension to add Deno support to VS Code. If you happen to be using Webstorm like myself, you can install the Deno plugin to add Deno support to Webstorm.

Creating the components

Fresh has a really simple project structure. The islands folder is the place where you'd place your "island" components. The isolated Preact components add interactivity to your pages, unlike route components, which are located in the routes folder and are rendered on the server. The components folder is a generic folder for storing any reusable components that are used within islands or routes.

Home and Convert components

The Home and Convert components are page components that are located under routes/index.tsx and routes/convert.tsx, representing the / and the /convert routes, respectively. When you reach to one of those routes, Fresh will render the respective components on the server, and return the full HTML to the client. Both routes are similar in the manner that both use the ConverterForm island component. However, the /convert route has some extra functionality. It needs to perform the following actions server-side:

Parse the amount, from, and to query parameters
Use those parameters to execute a request toward the CurrencyScoop API
Show the result from the API to the user

interface Data {
  amount: number;
  from: string;
  to: string;
  convertedAmount: number;
}

const DEFAULT_CURRENCY = 'USD';

export const handler: Handlers<Data> = {
  async GET(req, ctx) {
    const url = new URL(req.url);
    const amount = Number(url.searchParams.get('amount')) || 0;
    const from = url.searchParams.get('from') || DEFAULT_CURRENCY;
    const to = url.searchParams.get('to') || DEFAULT_CURRENCY;
    const csResponse = await fetch(`https://api.currencyscoop.com/v1/convert?api_key=${Deno.env.get('API_KEY')}&from=${from}&to=${to}&amount=${amount}`)
    const csResult = await csResponse.json();
    return ctx.render({ convertedAmount: csResult.response.value, amount, from, to });
  },
};

export default function Convert({ data }: PageProps<Data>) {
  return (
    <main className="flex justify-center items-center h-screen">
      <div className="p-4 max-w-screen-md bg-white shadow-md rounded px-8 pt-6 pb-6">
        <ConverterForm amount={data.amount} from={data.from} to={data.to}></ConverterForm>
        <div className="font-medium">
          <span className="text-slate-200">{data.amount} {data.from} = </span><br/>
          <span className="text-2xl">{data.convertedAmount.toFixed(2)} {data.to}</span>
        </div>
      </div>
    </main>
  );
}

It does this through custom handlers which you can attach to any route. Handlers are functions in the form of Request => Response or Request => Promise<Response> that are called when a request is made to a particular route. You can return any kind of response in a custom handler (for example, a JSON), or you can render a component. In our case, we're parsing the query parameters and then fetching the latest currency exchange rate based on the query parameters.

One thing to note here is that we're using Deno.env.get() to obtain the API key from the environment. API keys such as this one are usually sensitive information, so it wouldn't be wise to hardcode it in the code.

Once we get the result from CurrencyScoop, this is passed in to the Convert component so it can be displayed to the user.

ConverterForm component

The ConverterForm component is an island component. Island components add interactivity to your app, and you can use them like any other client-side Preact component. This involves using hooks such as useState() to update the state of the component based on user interactions.

In our case, we will hook into the form's SubmitEvent, and then change the button's label from "Convert" to "Converting..." as an indicator to the user that the currency conversion is taking place.

const currencyCodes = Object.entries(supportedCurrencies.fiats).map(([, currency]) => currency.currency_code);

interface ConverterFormProps {
  amount?: number,
  from?: string,
  to?: string
}

export default function ConverterForm({ amount, from, to }: ConverterFormProps) {
  const [submitted, setSubmitted] = useState(false);
  const [form, setForm] = useState({
    amount,
    from,
    to,
  });

  return (
    <form className="" action="/convert" onSubmit={() => setSubmitted(true)}>
      <div className="flex">
        <AmountInput value={form.amount} onChange={(amount) => setForm({ ...form, amount })}></AmountInput>
        <CurrencySelect currencies={currencyCodes} defaultCurrency="USD" name="from" selectedCurrency={form.from}
                        label="From" onChange={(from) => setForm({ ...form, from })}></CurrencySelect>
        <CurrencySelect currencies={currencyCodes} defaultCurrency="EUR" name="to" selectedCurrency={form.to} label="To"
                        onChange={(to) => setForm({ ...form, to })}></CurrencySelect>
      </div>
      <div className="flex items-center justify-center px-2">
        <button
          className="bg-blue-500 hover:bg-blue-700 text-white font-bold py-2 px-4 rounded focus:outline-none focus:shadow-outline"
          type="submit" disabled={submitted}>
          {submitted ? 'Converting...' : 'Convert'}
        </button>
      </div>
    </form>
  )
}

AmountInput and CurrencySelect components

The AmountInput and CurrencySelect components are pure components that have no internal state and are simply containers for the text input and the select input elements. They are used by the ConverterForm component.

interface AmountInputProps {
  value?: number;
  onChange: (newValue: string) => void
}

export default function AmountInput({ value, onChange }: AmountInputProps) {
  return (
    <div className="mb-4 px-1">
      <label className="block text-gray-700 text-sm font-bold mb-2" htmlFor="amount">
        Amount
      </label>
      <input
        className="shadow appearance-none border rounded py-2 px-3 text-gray-700 leading-tight focus:outline-none focus:shadow-outline"
        id="amount" name="amount" type="number" placeholder="0.0" value={value || 0} required onChange={(e: any) => onChange(e.target.value)} />
    </div>
  );
}

interface CurrencySelectProps {
  name: string;
  currencies: string[];
  selectedCurrency?: string;
  defaultCurrency: string;
  label: string;
  onChange: (newValue: string) => void
}

export default function CurrencySelect({ name, currencies, defaultCurrency, selectedCurrency, label, onChange }: CurrencySelectProps) {
  return (
    <div className="mb-6 px-1">
      <label className="block text-gray-700 text-sm font-bold mb-2" htmlFor={name}>
        {label}
      </label>
      <select
        className="shadow appearance-none border rounded py-2 px-3 text-gray-700 leading-tight focus:outline-none focus:shadow-outline"
        id={name}
        name={name}
        onChange={(e: any) => onChange(e.target.value)}>
        {currencies.map((currency) => <option key={currency} selected={selectedCurrency ? selectedCurrency === currency : currency === defaultCurrency}
                                                 value={currency}>{currency}</option>)}
      </select>
    </div>
  );
}

Deployment

Deploying Fresh apps is super-easy using Deno Deploy. All you need to do is sign up and link the GitHub repository of the project you need to deploy, and that is all. In our case, we had just one extra step of defining the API_KEY environment variable, and that was pretty much it.

Conclusion

Once the app is uploaded to Deno Deploy, it is fully usable as can be seen in the video below:

The app is available at https://fresh-currency-converter.deno.dev/ - feel free to play around with it! If you'd like to check out the source code, please visit our GitHub repository.

The Fresh framework is a fantastic new framework that is fast, well-documented, and easy to use. We've been able to spin up our currency conversion app in less than half of the day. If you're looking for a new framework to pick for your next project, then Fresh should definitely be at the top of your list.

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.

We love helping teams with projects that have missed their deadlines or helping keep your strategic digital initiatives on course. Check out our case studies and our clients that trust us with their engineering.

About the author(s)

Dario Djuric
Dario is a full-stack engineer who has spent most of his career doing enterprise Java projects. He has always had a hidden passion for frontend, though -- and he is now able to pursue that passion at This Dot. He spends most of his free time with his two sons, but occasionally, he manages to squeeze in some casual sports activities such as jogging, cycling, and soccer.
@dario_djuric @dariodjuric

The HTML Dialog Element: Enhancing Accessibility and Ease of Use

The HTML Dialog Element: Enhancing Accessibility and Ease of Use Dialogs are a common component added to applications, whether on the web or in native applications. Traditionally there has not been a standard way of implementing these on the web, resulting in many ad-hoc implementations that don’t act consistently across different web applications. Often, commonly expected features are missing from dialogs due to the complexity of implementing them. However, web browsers now offer a standard dialog element. Why use the dialog element? The native dialog element streamlines the implementation of dialogs, modals, and other kinds of non-modal dialogs. It does this by implementing many of the features needed by dialogs for you that are already baked into the browser. This is helpful as it reduces the burden on the developer when making their applications accessible by ensuring that user expectations concerning interaction are met, and it can also potentially simplify the implementation of dialogs in general. Basic usage Adding a dialog using the new tag can be achieved with just a few lines of code. ` However, adding the dialog alone won’t do anything to the page. It will show up only once you call the .showModal() method against it. ` Then if you want to close it you can call the .close() method on the dialog, or press the escape key to close it, just like most other modals work. Also, note how a backdrop appears that darkens the rest of the page and prevents you from interacting with it. Neat! Accessibility and focus management Correctly handling focus is important when making your web applications accessible to all users. Typically you have to move the current focus to the active dialog when showing them, but with the dialog element that’s done for you. By default, the focus will be set on the first focusable element in the dialog. You can optionally change which element receives focus first by setting the autofocus attribute on the element you want the focus to start on, as seen in the previous example where that attribute was added to the close element. Using the .showModal() method to open the dialog also implicitly adds the dialog ARIA role to the dialog element. This helps screen readers understand that a modal has appeared and the screen so it can act accordingly. Adding forms to dialogs Forms can also be added to dialogs, and there’s even a special method value for them. If you add a element with the method set to dialog then the form will have some different behaviors that differ from the standard get and post form methods. First off, no external HTTP request will be made with this new method. What will happen instead is that when the form gets submitted, the returnValue property on the form element will be set to the value of the submit button in the form. So given this example form: ` The form element with the example-form id will have its returnValue set to Submit. In addition to that, the dialog will close immediately after the submit event is done being handled, though not before automatic form validation is done. If this fails then the invalid event will be emitted. You may have already noticed one caveat to all of this. You might not want the form to close automatically when the submit handler is done running. If you perform an asynchronous request with an API or server you may want to wait for a response and show any errors that occur before dismissing the dialog. In this case, you can call event.preventDefault() in the submit event listener like so: ` Once your desired response comes back from the server, you can close it manually by using the .close() method on the dialog. Enhancing the backdrop The backdrop behind the dialog is a mostly translucent gray background by default. However, that backdrop is fully customizable using the ::backdrop pseudo-element. With it, you can set a background-color to any value you want, including gradients, images, etc. You may also want to make clicking the backdrop dismiss the modal, as this is a commonly implemented feature of them. By default, the <dialog> element doesn’t do this for us. There are a couple of changes that we can make to the dialog to get this working. First, an event listener is needed so that we know when the user clicks away from the dialog. ` Alone this event listener looks strange. It appears to dismiss the dialog whenever the dialog is clicked, not the backdrop. That’s the opposite of what we want to do. Unfortunately, you cannot listen for a click event on the backdrop as it is considered to be part of the dialog itself. Adding this event listener by itself will effectively make clicking anywhere on the page dismiss the dialog. To correct for this we need to wrap the contents of the dialog content with another element that will effectively mask the dialog and receive the click instead. A simple element can do! ` Even this isn’t perfect though as the contents of the div may have elements with margins in them that will push the div down, resulting in clicks close to the edges of the dialog to dismiss it. This can be resolved by adding a couple of styles the the wrapping div that will make the margin stay contained within the wrapper element. The dialog element itself also has some default padding that will exacerbate this issue. ` The wrapping div can be made into an inline-block element to contain the margin, and by moving the padding from the parent dialog to the wrapper, clicks made in the padded portions of the dialog will now interact with the wrapper element instead ensuring it won’t be dismissed. Conclusion Using the dialog element offers significant advantages for creating dialogs and modals by simplifying implementation with reasonable default behavior, enhancing accessibility for users that need assistive technologies such as screen readers by using automatic ARIA role assignment, tailored support for form elements, and flexible styling options....

Oct 25, 2024

4 mins

HTMLJavaScript

Making Seamless Page Transitions with the View Transitions API

Make Seamless Page Transitions using the View Transitions API Traditionally web applications have always had a less polished experience, both functionally and visually speaking, compared to native applications on mobile and other platforms. This has been improving over the years with the introduction of new web APIs and standards. One such new API that bridges that gap is the View Transitions API. What is the View Transitions API? The View Transitions API is a new browser feature that allows developers to more easily create animated transitions between pages and views, similar to how mobile apps have transitions when navigating between pages. Adding view transitions to your application can reduce the cognitive load on your users and make the experience feel less inconsistent. One great thing about view transitions is that they can be used by both SPAs (single-page applications) and MPAs (multi-page applications) alike! Using the View Transitions API for SPAs Let’s see how we can use view transitions ourselves. We will use examples adapted from demos created by the wonderful Jake Archibald and Bramus. There are some alterations to a few of the examples to make them work with the newest version of the View Transitions API, but otherwise, they’re mostly the same. The process of getting view transitions working for SPAs is as simple as calling document.startViewTransition right before starting navigation and replacing your page’s content immediately after that. You need to make this call in your router or in an event listener that triggers your page navigation. The following is an example of how you can hook into page navigation in a vanilla JavaScript application. This example uses the Navigation API if it’s available. As of the time of writing this article only Chromium-based browsers support the Navigation API, but there is a fallback to using a click listener on link elements so that this works with Firefox and Safari. ` If you’re using a framework, then there’s probably a better way to do this specific to that framework than by using this contrived example. For example, if you are implementing usage of this API with a Next application, you may opt for something like next-view-transitions. For this article, we’re going to focus on the way this is done in vanilla JavaScript so that the fundamentals of using the API are understood. Knowing how it’s implemented in vanilla JavaScript should give you enough understanding to implement this in the framework of your choice if there isn’t already a library that does it for you. Now we have a way to know when a navigation is being requested. Using the above utility function we can start the animation and replace our content as follows: ` getMyPageContentSomehow can be any function that returns HTML. How that is implemented will depend on your application and framework of choice. If you want to run these examples on your machine, the demo repository has instructions in its README. In essence, it’s as simple as hosting an HTTP server at the root of the project and visiting localhost. No fancy build system is required! By default, a fade is done that only lasts for a moment. The animation that happens can be configured using CSS with the ::view-transition-group pseudo-element on the element you want to animate, which in our case is the entire page, and we pass in root. ` Given that the animation properties are used, you have much control over what kind of animation to do. You can change the duration and the interpolation, add keyframes and gradients, and even add image masks. You can learn more about the animation properties in CSS on MDN. Using the View Transitions API for MPAs As mentioned, view transitions also work for MPAs with no client-side routing. Setting up view transitions for MPAs is much easier than for SPAs. All you have to do is include the CSS rule on all pages where you want the animations. ` Of course, like how it works with SPAs, you can customize the animations to your heart’s content using the view transition pseudo-elements. Conclusion I hope this article helped you understand the fundamentals of using the View Transitions API. Now that most browsers support it and it’s not too difficult to add it to existing applications, it is a great time to learn how to use it. You can view a full list of examples here (made by Jake Archibald and Bramus) if you want to see how advanced the animations can get. I like the Star Wars ones especially. The README explains how to get all the examples up and running (a total of 43!)....

Aug 2, 2024

4 mins

JavaScript

A Look at Playwright Parallelism

A Look at Playwright Parallelism Playwright is an open-source automation library developed by Microsoft, designed for testing web applications across multiple browsers. It enables developers and testers to write scripts that simulate real user actions when interacting with web pages. Playwright supports major browsers like Chrome, Firefox, and Safari, including their headless modes. Recently, it has gained a lot of popularity for its robustness, ease of use, and cross-browser compatibility. In this blog post, we will take a look at one very useful aspect of Playwright: running tests in parallel. Parallelism in Playwright Parallelism in Playwright refers to running multiple test spec files or even test cases within a spec file simultaneously, greatly improving test execution speed. This is achieved by running the tests in worker processes, where each worker process is an OS process, running independently, orchestrated by the test runner. All workers have identical environments, and each starts its own browser instance. Parallel execution is particularly beneficial in continuous integration and continuous deployment (CI/CD) pipelines, reducing overall build and testing times. Playwright's architecture inherently supports parallelism, and most modern test runners integrating with Playwright can leverage this feature. The parallel execution feature makes Playwright a highly efficient tool for large-scale web application testing. Enabling Parallelism By default, if you scaffold the project using npm init playwright@latest, parallelism is already enabled. Assuming that Playwright's configuration includes three browsers and there is a single spec file with two test cases, the total number of tests that Playwright needs to execute is 3x2 = 6. ` Playwright will decide on how many workers to use based on several factors: - Hardware support: Depending on the number of CPU cores and other system resources, the operating system will decide how many processes Playwright can spin up. - The workers property in the playwright.config.ts file. - The --workers argument to the playwright test command. For example, npx playwright test --workers 4. The --workers argument overrides the workers property in the configuration. However, in both cases, the number of workers can go up to the number of processes that Playwright can spin up, as decided by the operating system. Once it has determined the number of workers, and if the number of workers is larger than 1, Playwright will then decide how to split the work between workers. This decision also depends on several factors, such as the number of browsers involved and the granularity of the parallelism, which can be controlled in several ways: - In the test spec file, you can specify whether to run the test cases in parallel. To run tests in parallel, you can invoke test.describe.configure({ mode: 'parallel' }); before your test cases. - Alternatively, you can configure it per project by setting the fullyParallel: true property. - And finally, you can set it globally in the config, using the same property: fullyParallel: true. Therefore, if there is more than one worker and the parallel mode is enabled, Playwright will assign test cases to each worker as they become available. This scenario is ideal because it means that each test is stateless, and the resources are used most efficiently. ` Disabling Parallelism What if, however, the tests are not stateless? Imagine one test changes the global configuration of the app via some sort of administration page, and the configuration affects different parts of the app, like enabling or disabling features. Other tests, which may be testing those features, would be impacted and would report incorrect results. In such cases, you might want to disable parallelism. You can disable any parallelism globally by allowing just a single worker at any time. Following the instructions from the previous sections to configure the number of workers, you can either set the workers: 1 option in the configuration file or pass --workers=1 to the command line. ` Let's have a look at our test output in this case: ` Now, compare the time it took with one worker versus the time it took with four workers. It took 8.2 seconds with one worker compared to only 3.9 seconds with multiple workers. That might be an inefficient usage of resources, of course, especially if you have a large test suite and some of the tests are stateless and can be run without impacting other tests. Tweaking Parallelism If you want some tests not to run in parallel, but still want to utilize your workers, you can do that. Again, following the configuration options from the previous sections, you can annotate the entire spec file with test.describe.configure({ mode: 'serial' }); to have the tests run sequentially in that spec file, or use the fullyParallel: false property to run tests sequentially on the project level, or using the same property to run tests sequentially on the global level. This means you can still split the tests between workers, but the tests would be run sequentially within a worker depending on the configuration. For example, let's set the number of workers to 4, but set fullyParallel: false globally. ` The tests need to be run sequentially, but since each browser instance effectively provides an isolated environment, this means tests cannot impact each other between environments, and they are safe to be executed sequentially within an environment. This means setting fullyParallel: false on the global level is not the same as having workers: 1, since the browsers themselves offer an isolated environment for the tests to run sequentially. However, since we only have 3 environments (3 browsers), we cannot fully utilize 4 workers as we wanted, so the number of workers is 3. Conclusion In conclusion, Playwright's workers are the core of its parallelism capabilities, enabling tests to run concurrently across different environments and browsers with efficiency. Through its many configuration properties, Playwright allows you to configure parallelism at multiple levels, offering a granular approach to optimizing your test runs. Beyond just executing tests in parallel on a single machine, Playwright's parallelism can even extend to splitting work across multiple machines through sharding, significantly enhancing the scalability of your testing. We hope this blog post was useful. For those interested in delving deeper into the world of Playwright and its powerful features, we've also recently released a JS Drop titled Awesome Web Testing with Playwright, and we also hosted Debbie O'Brien from Microsoft in a Modern Web episode....

Mar 20, 2024

5 mins

JavaScriptPlaywrightTesting

Svelte 5 is Here!

Svelte 5 was finally released after a long time in development. Fortunately, we've been able to test it for some time, and now it has a stable release. Let's dig into its features and why this is such a significant change, even though Svelte 4 code is almost 100% compatible. Svelte syntax everywhere This is one of my favorite additions. Previously, Svelte syntax was limited to a component element. Refactoring code from a component and moving it to a JavaScript file worked differently. Now you can use the .svelte.js or .svelte.ts extension, which allows you to use the same syntax everywhere. It's important to note that it's a way to express that this is not just JS, and what you write may be compiled to something else, just like .svelte files are not just html even though they look very similar. Runes The introduction of runes is one of the most significant changes in Svelte. Many users felt attracted to variables being instantly reactive in previous versions. ` There was, however, a lot of magic underneath and a considerable amount of work from the compiler to make it behave reactively. $state In Svelte 5, a reactive variable has to be explicitly declared using the $state rune, which brings a clear distinction between what is reactive and what isn’t. ` In the previous code, $state is not an actual function being called; it's a hint for the compiler to do something special with this declaration. Rune names always start with a dollar sign ($) and do not need to be imported. However, there’s much more to the changes than just the way we declare reactive variables. Runes bring a lot of new features that make Svelte 5 a great improvement. In Svelte 5, objects or arrays use Proxies to allow for granular reactivity, meaning that individual properties in an object are reactive, even if they are nested objects or arrays. If you modify a property, it will only update that property and will not trigger an update on the whole object. It also supports triggering updates when methods like array.push are called. In previous versions, an assignment was required to trigger an update: ` To have a similar behavior of svelte 4 (no deep reactivity), use the $state.raw() rune. This syntax of .* is common for related features of a rune: $state.raw() will require an assignment to trigger reactivity. ` Because proxies are used, you may need to extract the underlying state instead of the proxy itself. In that case, $state.snapshot() should be used: ` $derived We will use $derived and $derived.by to declare a derived state. The two runes are essentially the same, except one allows us to use a function instead of an expression, allowing for more complex operations to calculate the derived values. ` $effect Effects are useful for running something triggered by a change in state. One of the things you'll note from the $effect rune is that dependencies don't need to be explicit. Those will be picked from reactive values read synchronously in the body of the effect function. ` Something to bear in mind is that these dependencies are picked each time the effect runs. The values read during the last run become the dependencies of the effect. ` Depending on the result of the random method, foo or bar will stop being a dependency of the effect. You should place them outside the condition so they can trigger reruns of the effect. *Variants* of the effect rune are $effect.pre, which runs before a DOM update, and $effect.tracking(), which checks for the context of the effect (true for an effect inside an effect or in the template). $props This rune replaces the export let keywords used in previous versions to define a component's props. To use the $props syntax, we can consider it to return an object with all the properties a component receives. We can use JavaScript syntax to destructure it or use the rest property if we want to retrieve every property not explicitly destructured.. ` $bindable If you want to mutate a prop so that the change flows back to the parent, you can use the $bindable prop to make it work in both directions. A parent component can pass a value to a child component, and the child component is able to modify it, returning the data back to the parent component. ` $inspect The $inspect rune only works in dev mode and will track dependencies deeply. By default, it will call console.log with the provided argument whenever it detects a change. To change the underlying function, use $inspect.with().with): ` $host The host rune gives access to the host element when compiling as a custom element: ` ` Other changes Another important change is that component events are just props in Svelte 5, so you can destructure them using the $props() rune: ` A special children property can be used to project content into a component instead of using slots. Inside the components, use the [@render[(https://svelte.dev/docs/svelte/@render) tag to place them. ` Optional chaining (?.) prevents from attempting to render it if no children are passed in. If you need to render different components in different places (named slots before Svelte 5, you can pass them as any other prop, and use @render with them. Snippets Snippets allow us to declare markup slices and render them conveniently using the render tag (@render). They can take any number of arguments. ` Snippets can also be passed as props to other components. ` ` Conclusion Some exciting changes to the Svelte syntax were introduced while, at the same time, maximum compatibility efforts were made. This was a massive rewrite with numerous improvements in terms of performance, bundle size, and DX. Besides that, a new CLI has been released, making the whole experience of starting a project or adding features delightful. If you haven't tried Svelte before, it's a great time to try it now....

Nov 27, 2024

4 mins

Svelte

Let's innovate together!

We're ready to be your trusted technical partners in your digital innovation journey.

Whether it's modernization or custom software solutions, our team of experts can guide you through best practices and how to build scalable, performant software that lasts.

Building Your First App Using Fresh Framework

The App Architecture

Getting API Key from CurrencyScoop

Scaffolding the Fresh app

Creating the components

Home and Convert components

ConverterForm component

AmountInput and CurrencySelect components

Deployment

Conclusion

Dario Djuric

You might also like

The HTML Dialog Element: Enhancing Accessibility and Ease of Use

Making Seamless Page Transitions with the View Transitions API

A Look at Playwright Parallelism

Svelte 5 is Here!

Let's innovate together!

You might also like

The HTML Dialog Element: Enhancing Accessibility and Ease of Use

Making Seamless Page Transitions with the View Transitions API

A Look at Playwright Parallelism

Svelte 5 is Here!