Javascript

Basic RxJS Operators and How to Use Them

Published Dec 2, 2020

Updated Feb 14, 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This article was written over 18 months ago and may contain information that is out of date.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.

In our Getting Started With RxJS article, we briefly mentioned Operators. In this article, we will expand further on what Operators are in RxJS. We will also show you some basic Operators, what they do, and how you can use them.

What are RxJS Operators?

Taken straight from the RxJS manual:

Operators are the essential pieces that allow complex asynchronous code to be easily composed in a declarative manner.

If you're scratching your head, don't worry. I think most people would be confused by that statement alone. Luckily for us, the manual gives an even better definition:

An Operator is a function which creates a new Observable based on the current Observable. This is a pure operation: the previous Observable stays unmodified.

Essentially, an Operator is like a machine that takes an Observable as an input, performs some logic on the values streamed through the Observable, and creates a new Observable with these values, without changing the original Observable.

The diagram below might help illustrate it a little better.

We can see that the Operator takes in the values from one Observable, and creates a new Observable that emits altered values of the original Observable's values, without affecting the original Observable.

Now let's take a look at 6 basic Operators: of, from, map, tap, switchMap, take.

1. `of` - Creation Operator

The of Operator is a creation Operator. Creation Operators are functions that create an Observable stream from a source.

The of Operator will create an Observable that emits a variable amount of values in sequence, followed by a Completion notification.

A Completion notification tells the Observable's subscribers that the Observable will no longer be emitting new values. We will cover this in more detail in a future article!

Let's take a look at of in practice.

const arr = [1, 2, 3];

const arr$ = of(arr);

arr$.subscribe((values) => console.log(`Emitted Values: `, values));

of creates the Observable, and when we subscribe to it, it starts emitting its values immediately.

The output of the above is:

Emitted Values: [1, 2, 3]

of will emit the full array [1, 2, 3] as a full value. This is in contrast to from, which we will look at next!

2. `from` - Creation Operator

The from Operator turns an Array, Promise, or Iterable, into an Observable.

This operator will convert a Promise to an Observable, allowing for it to be handled in a more reactive manner. When the Promise resolves or rejects, a completion notification will be sent to any subscribers.

Also, unlike of, it will emit each element in an Array or Iterable in sequence, rather than the full value. Once all elements of the Array or Iterable have been emitted, a completion notification is sent to any subscribers.

Let's take the example we used for of to see this difference in action:

const arr = [1, 2, 3];

const arr$ = from(arr);

arr$.subscribe((values) => console.log(`Emitted Values: `, values));

Its output is:

Emitted Values:  1
Emitted Values:  2
Emitted Values:  3

As we can see by the multiple logs, the from Operator took each number and emitted it as a value. The subscriber received each value in sequence, and called console.log three times.

We can also use a value such as a string:

const fromString$ = from("Hello");
fromString$.subscribe((value) => console.log(`Emitted Values: `, value));

The output is:

Emitted Values:  H 
Emitted Values:  e 
Emitted Values:  l 
Emitted Values:  l 
Emitted Values:  o

How about for a Promise? Let's take a look!

const examplePromise = new Promise((resolve, reject) => {
  // Do some async code and resolve and object with an id property
  return resolve({ id: 1 });
});

const promise$ = from(examplePromise);
promise$.subscribe((value) => console.log(`Emitted Values: `, value));

The output of this would be:

Emitted Values:  {id: 1}

When the Promise resolves, the value gets emitted as the next value in the Observable.

3. `map` - Transformation Operator

The map operator is a Transformation Operator. It takes values from one Observable, transforms them, and creates a new Observable that emits the transformed values.

With map, you can perform simple transformations to the values emitted by an Observable. Let's take a look at two examples.

For the first example, we'll take the Array example for the from Operator, and modify it to also use map:

const arr = [1, 2, 3];

const fromArr$ = from(arr);

fromArr$
  .pipe(map((value) => value + 10))
  .subscribe((value) => console.log(`Emitted Values: `, value));

You'll notice the introduction of the .pipe() call. This is RxJS's method for applying operators to an Observable's stream before you subscribe to it. It will pipe the value emitted from the Observable through each operator passed as an argument, before passing the final transformed value to the subscribe method. We'll cover this in more detail in a future article!

In this example, as map is a transformation Operator, it must be used within the .pipe() call so that it can transform the value it receives from the Observable. We are simply adding 10 to the value, and emitting the transformed value.

You can see this in the output:

Emitted Values:  11
Emitted Values:  12
Emitted Values:  13

We can do almost anything in the map Operator, but a common use-case would be to get a property from an object that is emitted in an Observable stream. We can use our Promise example to see this in action:

const examplePromise = new Promise((resolve, reject) => {
  // Do some async code and resolve and object with an id property
  return resolve({ id: 1 });
});

const promise$ = from(examplePromise);
promise$
  .pipe(map((obj) => obj.id))
  .subscribe((value) => console.log(`Emitted Values: `, value));

Here, we are telling the map operator to return the id property of the object that is resolved in the Promise. The output of this is:

Emitted Values:  1

The map Operator is a commonly used Operator and is very useful for a number of use-cases!

4. `switchMap` - Transformation Operator

The switchMap operator is another transformation Operator.

switchMap receives the values emitted by an Observable, and then returns a new Observable from a different source.

Let's say you have an Observable that emits User IDs. You may want to fetch the full User object correlating to the ID, then do something with the full details. The switchMap operator would receive the ID from the Observable, then return an Observable containing the response from the request to fetch the User object.

I find it can be useful to think of this in the terms of switching streams. You're switching from one Observable stream to another.

Let's take a look at an example:

const userDetails$ = from(this.userService.getActiveUserID())
    .pipe(switchMap(id => this.userService.fetchUserForID(id)))
    .subscribe(user => console.log("Found user ", user));

Here, we ask for the active user's ID. Then, we ask the userService to make an ajax request to our backend to fetch the User that correlates with the ID. We are assuming that the fetchUserForID call returns an Observable. (This can be possible with the ajax operator which we will discuss in a future article!)

We then subscribe to this new Observable stream, and receive the value it emits, rather than the values emitted from from(this.userService.getActiveUserID()) as seen in the output:

Found user  {id: 1, name: "Test User", email: "test@test.com"}

It's worth noting that the switchMap operator will cancel any in-flight network requests if it receives a new value from the original (commonly known as the source) Observable stream, making it a great candidate for typeahead search implementations!

5. `tap` - Utility Operator

The tap Operator is a Utility Operator which is very similar to a helper function, except in the reactive programming landscape.

tap allows you to perform actions or side effects on an Observable stream without modifying or altering the original stream. The values "pass-through" the tap Operator to the next Operator or Subscriber.

This can be very useful for logging:

const arr = [1, 2, 3];

const fromArr$ = from(arr);

fromArr$
  .pipe(tap((value) => console.log("Received value: ", value)))
  .subscribe((value) => console.log(`Emitted Values: `, value));

Which would output:

Received value:  1
Emitted Values:  1

Received value:  2
Emitted Values:  2

Received value:  3
Emitted Values:  3

6. `take` - Filtering Operator

The take operator is a Filtering Operator. Filtering Operators allows you to select how and when to accept values emitted from Observables.

take is one of the most common and most simplistic filtering Operators. It allows you to specify a maximum number of values you want to receive from an Observable.

We can use our from example where we emit the elements of an Array, and combine it with take to get a better understanding of this operator:

const arr = [1, 2, 3];

const fromArr$ = from(arr);

fromArr$
  .pipe(take(1))
  .subscribe((value) => console.log(`Emitted Values: `, value));

From the output below we can see we only received and used 1 value from the array:

Emitted Values:  1

It can be used in situations where we want to limit how many user-produced events (fromEvent) we want to handle, for example, the first time the user clicks in our app.

Conclusion

In this article, we briefly covered some of what I would consider to be the most common Operators that live in RxJS. By understanding these 6 Operators, you are on your way to mastering RxJS! Stay tuned for more articles discussing more operators and more in-depth topics based on RxJS.

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)

Colum Ferry
JavaScript Developer and Enthusiast. Really enjoy working with Angular. Married with 2 amazing kids. Powered by Coffee.
@FerryColum @https://github.com/coly010

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

SSR Finally a First-Class Citizen in Angular?

I am sure you've already heard about server-side rendering (SSR). Generally, it's a technique used to deliver the HTML content generated by the server to the client. The client-side JavaScript framework then hydrates that HTML content to provide a fully interactive application. SSR provides numerous benefits if used correctly, including improved initial load times, better content indexing by search engines, and improved performance on lower-tier devices. Driven by the need for faster, more efficient web applications, with the rise in popularity of Node.js and, thus, server-side JavaScript, SSR has become a de facto standard in modern web development frameworks. At first, SSR was being provided as a part of meta-frameworks like Next.js, Nuxt, or Analog.js. Then, React introduced React Server Components, which marked a significant milestone in the way we think about front-end development. We think of front-end frameworks as being effectively full-stack, and a purely SPA approach is falling out of favor. However, I'm willing to bet that if you're a developer focused mostly on Angular, you may not have heard as much about SSR as your React counterparts. For a long time, Angular has been mostly focused on the SPA approach, and while we had Angular Universal or Analog.js, it was not as widely adopted. And that makes sense, given that Angular was widely regarded as best suited for complex, interactive applications, such as SaaS products or internal company tools, where SEO and initial load times were not as critical as they are for consumer-facing applications. Nevertheless, we have been blessed with the so-called Angular Renaissance, which has, among other things, brought SSR to the forefront of Angular development with the @angular/ssr package. Let's look at what Angular SSR is, how it works, and how you can get started. @angular/ssr The @angular/ssr package is not new; it was written from scratch. It's still Angular Universal. However, it's been pulled into the Angular CLI repository, and the appropriate schematics have been added to make it easier to use. What that means is that you can now add SSR to your Angular application with a single command: ` and you can generate a new SSR application with: ` And to make SSR a first-class citizen, the Angular team is planning to make it the default in the next version. But surely, it's not only rebranding and some CLI commands, you may say. And you're right. You may remember that hydration in Angular Universal has not been optimal as it was destructive and required essentially a complete re-render of the application, thus pretty much negating the benefits of SSR. With the introduction of non-destructive hydration in Angular 16 and its stability in Angular 17, the Angular team has taken a significant step forward in making SSR a first-class citizen. How to Make an SSR-capable Angular Application Let's look at how to use Angular SSR in practice by creating a simple SSR app. First, we need to create a new Angular application with SSR support: ` That will generate a few server-specific files: - server.ts, which is an Express server configured to handle Angular SSR requests by default but can also be extended to handle API routes, or anything else that Express can handle. - src/app/app.config.server.ts provides configuration for the server application similar to your app.config.ts, which defines the configuration for your client application. Both export an instance of ApplicationConfig - src/main.server.ts bootstraps the server application in a similar way to what main.ts does for your client app by calling the bootstrapApplication function. You should have an SSR application ready just like that. You can verify that by running ng serve. The terminal output should show you information about the server bundles generated, and you should be able to see the default app when going to http://localhost:4200. Open the Developer Tools and check the console to see that hydration is enabled. You'll see a message with hydration-related stats, such as the number of components and nodes hydrated. Speaking of hydration... Client Hydration If you open the src/app/app.config.ts in your new SSR application, you'll notice one interesting provider: provideClientHydration(). This provider is crucial for enabling hydration - a process that restores the server-side rendered application on the client. Hydration improves application performance by avoiding extra work to re-create DOM nodes. Angular tries to match existing DOM elements to the application's structure at runtime and reuses DOM nodes when possible. This results in a performance improvement measured using Core Web Vitals statistics, such as reducing the Interaction To Next Paint (INP), Largest Contentful Paint (LCP), and Cumulative Layout Shift (CLS). Improving these metrics also positively impacts SEO performance. Without hydration enabled, server-side rendered Angular applications will destroy and re-render the application's DOM, which may result in visible UI flicker, negatively impact Core Web Vitals like LCP, and cause layout shifts. Enabling hydration allows the existing DOM to be reused and prevents flickering. Event Replay and Improved Debugging With Angular 18, event replay, a feature that significantly enhances the SSR experience, came into developer preview. Event replay captures user interactions during the SSR phase and replays them once the application is hydrated. This ensures that user actions, such as adding items to a cart, are not lost during the hydration process, providing a seamless user experience even on slow networks. To enable event replay, you can add withEventReplay to your provideClientHydration call: ` Furthermore, Angular 18 takes another step towards making SSR a first-class citizen by enhancing the debugging experience with Angular DevTools. Now, DevTools include overlays and detailed error breakdowns, empowering developers to visualize and troubleshoot hydration issues directly in the browser. Constraints However, hydration imposes a few constraints on your application that are not present without hydration enabled. Your application must have the same generated DOM structure on both the server and the client. The hydration process expects the DOM tree to have the same structure in both environments, including whitespaces and comment nodes produced during server-side rendering. Direct DOM Manipulation The fact that server and client DOM structures must match means that components that manipulate the DOM using native DOM APIs or use innerHTML or outerHTML will encounter hydration errors. The errors are thrown because Angular is unaware of these changes and cannot resolve them during hydration. Examples include accessing the document, querying for specific elements, and injecting additional nodes using appendChild. Detaching DOM nodes and moving them to other locations will also cause errors. Direct DOM manipulation is generally considered bad practice in Angular, so I recommend refactoring your components to avoid it regardless of hydration. However, in warranted cases where refactoring is not feasible, you can use the ngSkipHydration attribute until a hydration-friendly solution can be implemented. You can use it directly in a template: ` or as a host binding: ` > Note: The ngSkipHydration attribute forces Angular to skip hydrating the entire component and its children. So use this attribute carefully, as, for example, applying it to your root application component would effectively disable hydration for the entire application. Valid HTML Structure Another constraint is that invalid HTML structures in component templates can result in DOM mismatch errors during hydration. Common issues include: - without a - inside a - inside an - inside another Again, if you have an invalid HTML, you should fix this regardless of hydration. If you are unsure about your HTML's validity, you can use the W3 validator to check it. Zoneless apps or custom Zone.js Hydration relies on a signal from Zone.js when it becomes stable. Custom or "noop" Zone.js implementations may thus disrupt the timing of this event, triggering the serialization or cleanup process too early or too late. This configuration is not yet fully supported. While Zoneless is already available in developer preview and we could assume this issue will be resolved when it lands as stable, there is no explicit ETA mentioned in the official roadmap. I18n One of the biggest blockers for adoption of client hydration was the lack of support for internationalization with hydration. By default, Angular 17 skipped hydration for components that used i18n blocks, re-rendering them from scratch. In Angular 18, however, hydration for i18n blocks got into developer preview. To enable hydration for i18n blocks, you can add withI18nSupport to your provideClientHydration call. ` Third-Party Libraries with DOM Manipulation The last thing to consider is third-party libraries that manipulate DOM, such as D3 charts. They could cause DOM mismatch errors when hydration is enabled. You can use the ngSkipHydration attribute to skip hydration for components rendered using these libraries. Conclusion The Angular team has been doing great work to make the framework more modern and competitive, hearing the community feedback and adjusting the roadmap accordingly. And SSR is an excellent example of that. With the introduction of non-destructive hydration in Angular 16 and making it stable in Angular 17, the Angular team has taken a significant step forward in making SSR a first-class citizen in Angular. The @angular/ssr package is now part of the Angular CLI, making adding SSR to your Angular application easier. The Angular team plans to make SSR the default in the next version, further solidifying its position in the Angular ecosystem. However, as with any new feature, there are some constraints and best practices to follow when using SSR with Angular. You should be aware of hydration's limitations and ensure your application is compatible with it. However, if you follow the guidelines provided by the Angular team, you should be able to take advantage of the benefits of SSR without any significant issues....

Jun 26, 2024

8 mins

AngularJavaScriptExpress.js

Mapping Returned HTTP Data with RxJS

In frontend development, it's likely that you will make API requests to retrieve data from some backend resource. However, some backends are set up in such a way that they either send too much data or not enough data back. When we combine what we know already about Reactive Programming and RxJS, we can handle these situations in a very elegant manner using some useful operators that RxJS provides us. In this article, we will look at handling both scenarios and look at four operators in particular: map, mergeMap, concatMap and switchMap. We will also provide links to some StackBlitz examples so you can see these live. For fun, we'll use the Star Wars API to fetch data and use Angular as our Frontend framework of choice as its HTTP library has Reactive Bindings out of the box. Handling too much data (part 1) Ok, let's set up the scenario. We want to find out some details about Luke Skywalker such as his name, birth year, height, weight, and eye color. With Angular, we can do this by simply making an HTTP request: ` If we do this, we _do_ get back the info we need, but we _also_ get back a lot of info we _don't_ need such as when the API entry was created and edited, Luke's species, his Vehicles etc. Right now, we don't care about those details. Let's see how we could use RxJS's map operator to only return the data we want. ` We can see from the example above that it's super easy to only pull the values you need from the response object! Note You can also see how we managed to map some of the fields in the response from snake_case to camelCase which is more of a convention in JavaScript _as well as_ mapping some fields in the response to a new name (mass -> weight). We can also convert some types to other types, such as mass as string to weight as number. This can be super helpful to keep the domain language of your frontend codebase intact. Live Example You can check this code out in action over at the live example here on StackBlitz. Feel free to fork it and play with it. Handling too much data (part 2) Another common use case of having too much data is search results. Some times we only want to display the first result from a bunch of search results. Let's set up a new scenario. We'll create a typeahead search that only shows the most relevant search result. We want to request search results after every key press the user makes; however, we also don't want to make requests that are not needed. Therefore, we want to cancel any inflight requests created as the user types. For this scenario, we'll be using a mix of the map and switchMap operators. We'll also use Angular's Reactive Forms Module to provide us with some reactive bindings. Our code for this is very simple: ` It's that simple to create an eager typeahead search with Angular and RxJS. You can see the live example of this here on StackBlitz. Handling too little data We've looked at how to handle too much data in the API response with RxJS, but how about when we have too little data? We can build this scenario out perfectly with the Star Wars API. Let's say we want to see what films the characters we are searching for appear in. The API response for the characters _does_ contain what films they are in, but it _does not_ give us details, just a URL that we can send a new request to get that film's data. This is also an Array of films so we _may_ want to get the details for all the films they appear in at this time. Let's see how we can transform our search code to allow us to fetch more data _related_ to the results and map it into the final object that we use to render the data. ` I highly recommend reading the code above and the comments to understand exactly how to achieve this scenario. This pattern is very powerful, especially for example if you need to iterate over an array of user IDs and fetch the user details associated with those IDs. There is also a live example of this here on StackBlitz that you can use to try it out. Conclusion This is a small introduction to mapping data returned from HTTP requests with RxJS, but hopefully you can see use this as a reference point if you ever need to perform complex data mapping that involves additional API requests....

Jan 4, 2021

4 mins

RxJSAngularJavaScript

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

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Basic RxJS Operators and How to Use Them

What are RxJS Operators?

1. `of` - Creation Operator

2. `from` - Creation Operator

3. `map` - Transformation Operator

4. `switchMap` - Transformation Operator

5. `tap` - Utility Operator

6. `take` - Filtering Operator

Conclusion

Colum Ferry

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You might also like

The HTML Dialog Element: Enhancing Accessibility and Ease of Use

SSR Finally a First-Class Citizen in Angular?

Mapping Returned HTTP Data with RxJS

Svelte 5 is Here!

What are RxJS Operators?

1. of - Creation Operator

2. from - Creation Operator

3. map - Transformation Operator

4. switchMap - Transformation Operator

5. tap - Utility Operator

6. take - Filtering Operator

Conclusion

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SSR Finally a First-Class Citizen in Angular?

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Svelte 5 is Here!

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The HTML Dialog Element: Enhancing Accessibility and Ease of Use

SSR Finally a First-Class Citizen in Angular?

Mapping Returned HTTP Data with RxJS

Svelte 5 is Here!

1. `of` - Creation Operator

2. `from` - Creation Operator

3. `map` - Transformation Operator

4. `switchMap` - Transformation Operator

5. `tap` - Utility Operator

6. `take` - Filtering Operator