Angular

Content Projection in Angular

Published Jan 4, 2022

Updated Feb 13, 2023

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This article was written over 18 months ago and may contain information that is out of date.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

Imagine yourself at a movie theater. No matter what theater you go to, or what movie you see, you'll notice some very similar things - most notably, the large screen the movie plays on. This screen is an excellent example of a reusable object - it can show any movie projected onto it! The screen doesn't need to know the details of the movie it's playing - all it does is show whatever content is projected onto it.

This is a similar idea to how content projection works in web development! Today, we'll go over what content projection looks like and how you can use it to make components that are reusable and less tied to the data they display.

We'll be using Angular for these examples, but any framework you'd like to use likely has a way to do this as well!

If you'd like to view the source code for these examples, you can check them out in this Stackblitz editor.

Single slot projection

The simplest way to do content projection is to use a single "slot" or area where we pass data in. Note that you're not limited on what data you pass in - you could provide as much data as you wanted in here. But your component that's handling the content projection uses a single slot for all that data.

Using the movie example above, let's create a simple "screen" that will display a random cat GIF, and some "now playing" text with it.

For the screen component, the HTML will be very simple - just a section container and a special Angular tag called ng-content. This element acts as a placeholder for the content that will be passed into it, and does not create a DOM element itself. It tells the component that we expect some data in an unknown shape to be shown in it's place.

// single-screen.component.html
<section>
  <ng-content></ng-content>
</section>

Then, in our main app component, we can send this screen the data we want it to show!

// app.component.html
<app-single-screen>
  <div class="movie">
    <img src="https://cataas.com/cat/gif" />
  </div>
  <div class="now-playing">
    <h2>Now Playing: Random Cat GIF!</h2>
  </div>
</app-single-screen>

And that's it - our single-screen component will display the GIF and title!

Multi-slot projection

Sometimes, it can be useful to designate some of the data that gets projected into certain sections of our component. In the previous example, we could have the "Now Playing" text set up almost anywhere - it could be on the top of the screen, the bottom, over the image itself. Even though we're projecting data into our component, we can designate some sections with a particular name, so when we write the content that gets sent to the component, we can tell it where to go.

If we wanted to set up our screen so that it always shows the name first and then the image in our component, we would specify the select value on the ng-content tag. If we want one of these tags to be the default value, we can leave its select value empty.

// multi-screen.component.html
<section>
  <ng-content></ng-content>
  <ng-content select="[movie]"></ng-content>
</section>

Then, when we add this tag to our main app, we'll see the data in the order our component says it should show, no matter what order we type it in.

// app.component.html
<app-multi-screen>
  <div class="movie" movie>
    <img src="https://cataas.com/cat/gif?tags=silly" />
  </div>
  <div class="now-playing">
    <h2>Now Playing: Random Cat GIF!</h2>
  </div>
</app-multi-screen>

In conclusion

This topic can be as simple or as complex as you need it to. There's tons of great use cases for content projection. You could use it to create reusable layouts, as an expansion toggle wrapper around different lists of data, or to create reusable designed pieces that can take in whatever type of data you'd like. If you're interested in some more complex examples, I'd highly recommend checking out the Angular documentation for this subject. Can you think of other great use cases? Let us know!

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Linda Thompson
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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

Exploring Angular Forms: A New Alternative with Signals

Exploring Angular Forms: A New Alternative with Signals In the world of Angular, forms are essential for user interaction, whether you're crafting a simple login page or a more complex user profile interface. Angular traditionally offers two primary approaches: template-driven forms and reactive forms. In my previous series on Angular Reactive Forms, I explored how to harness reactive forms' power to manage complex logic, create dynamic forms, and build custom form controls. A new tool for managing reactivity - signals - has been introduced in version 16 of Angular and has been the focus of Angular maintainers ever since, becoming stable with version 17. Signals allow you to handle state changes declaratively, offering an exciting alternative that combines the simplicity of template-driven forms with the robust reactivity of reactive forms. This article will examine how signals can add reactivity to both simple and complex forms in Angular. Recap: Angular Forms Approaches Before diving into the topic of enhancing template-driven forms with signals, let’s quickly recap Angular's traditional forms approaches: 1. Template-Driven Forms: Defined directly in the HTML template using directives like ngModel, these forms are easy to set up and are ideal for simple forms. However, they may not provide the fine-grained control required for more complex scenarios. Here's a minimal example of a template-driven form: ` ` 2. Reactive Forms: Managed programmatically in the component class using Angular's FormGroup, FormControl, and FormArray classes; reactive forms offer granular control over form state and validation. This approach is well-suited for complex forms, as my previous articles on Angular Reactive Forms discussed. And here's a minimal example of a reactive form: ` ` Introducing Signals as a New Way to Handle Form Reactivity With the release of Angular 16, signals have emerged as a new way to manage reactivity. Signals provide a declarative approach to state management, making your code more predictable and easier to understand. When applied to forms, signals can enhance the simplicity of template-driven forms while offering the reactivity and control typically associated with reactive forms. Let’s explore how signals can be used in both simple and complex form scenarios. Example 1: A Simple Template-Driven Form with Signals Consider a basic login form. Typically, this would be implemented using template-driven forms like this: ` ` This approach works well for simple forms, but by introducing signals, we can keep the simplicity while adding reactive capabilities: ` ` In this example, the form fields are defined as signals, allowing for reactive updates whenever the form state changes. The formValue signal provides a computed value that reflects the current state of the form. This approach offers a more declarative way to manage form state and reactivity, combining the simplicity of template-driven forms with the power of signals. You may be tempted to define the form directly as an object inside a signal. While such an approach may seem more concise, typing into the individual fields does not dispatch reactivity updates, which is usually a deal breaker. Here’s an example StackBlitz with a component suffering from such an issue: Therefore, if you'd like to react to changes in the form fields, it's better to define each field as a separate signal. By defining each form field as a separate signal, you ensure that changes to individual fields trigger reactivity updates correctly. Example 2: A Complex Form with Signals You may see little benefit in using signals for simple forms like the login form above, but they truly shine when handling more complex forms. Let's explore a more intricate scenario - a user profile form that includes fields like firstName, lastName, email, phoneNumbers, and address. The phoneNumbers field is dynamic, allowing users to add or remove phone numbers as needed. Here's how this form might be defined using signals: ` > Notice that the phoneNumbers field is defined as a signal of an array of signals. This structure allows us to track changes to individual phone numbers and update the form state reactively. The addPhoneNumber and removePhoneNumber methods update the phoneNumbers signal array, triggering reactivity updates in the form. ` > In the template, we use the phoneNumbers signal array to dynamically render the phone number input fields. The addPhoneNumber and removePhoneNumber methods allow users to reactively add or remove phone numbers, updating the form state. Notice the usage of the track function, which is necessary to ensure that the ngFor directive tracks changes to the phoneNumbers array correctly. Here's a StackBlitz demo of the complex form example for you to play around with: Validating Forms with Signals Validation is critical to any form, ensuring that user input meets the required criteria before submission. With signals, validation can be handled in a reactive and declarative manner. In the complex form example above, we've implemented a computed signal called formValid, which checks whether all fields meet specific validation criteria. The validation logic can easily be customized to accommodate different rules, such as checking for valid email formats or ensuring that all required fields are filled out. Using signals for validation allows you to create more maintainable and testable code, as the validation rules are clearly defined and react automatically to changes in form fields. It can even be abstracted into a separate utility to make it reusable across different forms. In the complex form example, the formValid signal ensures that all required fields are filled and validates the email and phone numbers format. This approach to validation is a bit simple and needs to be better connected to the actual form fields. While it will work for many use cases, in some cases, you might want to wait until explicit "signal forms" support is added to Angular. Tim Deschryver started implementing some abstractions around signal forms, including validation and wrote an article about it. Let's see if something like this will be added to Angular in the future. Why Use Signals in Angular Forms? The adoption of signals in Angular provides a powerful new way to manage form state and reactivity. Signals offer a flexible, declarative approach that can simplify complex form handling by combining the strengths of template-driven forms and reactive forms. Here are some key benefits of using signals in Angular forms: 1. Declarative State Management: Signals allow you to define form fields and computed values declaratively, making your code more predictable and easier to understand. 2. Reactivity: Signals provide reactive updates to form fields, ensuring that changes to the form state trigger reactivity updates automatically. 3. Granular Control: Signals allow you to define form fields at a granular level, enabling fine-grained control over form state and validation. 4. Dynamic Forms: Signals can be used to create dynamic forms with fields that can be added or removed dynamically, providing a flexible way to handle complex form scenarios. 5. Simplicity: Signals can offer a simpler, more concise way to manage form states than traditional reactive forms, making building and maintaining complex forms easier. Conclusion In my previous articles, we explored the powerful features of Angular reactive forms, from dynamic form construction to custom form controls. With the introduction of signals, Angular developers have a new tool that merges the simplicity of template-driven forms with the reactivity of reactive forms. While many use cases warrant Reactive Forms, signals provide a fresh, powerful alternative for managing form state in Angular applications requiring a more straightforward, declarative approach. As Angular continues to evolve, experimenting with these new features will help you build more maintainable, performant applications. Happy coding!...

Oct 4, 2024

5 mins

AngularJavaScript

Introducing the Vue 3 and XState kit for starter.dev

*Starter.dev is an open source community resource developed by This Dot Labs that provides code starter kits in a variety of web technologies, including React, Angular, Vue, etc. with the hope of enabling developers to bootstrap their projects quickly without having to spend time configuring tooling.* Intro Today, we’re delighted to announce a new starter kit featuring Vue and XState! In this blog post, we’ll dive into what’s included with the kit, how to get started using it, and what makes this kit unique. What’s included All of our kits strive to provide you with popular and reliable frameworks and libraries, along with recommended tooling all configured for you, and designed to help you spin your projects up faster. This kit includes: - Vue as the core JS framework - XState for managing our application’s state - CSS for styling - Cypress component testing - Vue Router to manage navigation between pages - Storybook for visual prototyping - ESlint and Prettier to lint and format your code How to get started using the kit To get started using this kit, we recommend the starter CLI tool. You can pass in the kit name directly, and the tool will guide you through naming your project, installing your dependencies, and running the app locally. Each kit comes with some sample components, so you can see how the provided tooling works together right away. ` Now let’s dive into some of the unique aspects of this kit. Vue 3 Vue is a very powerful JS framework. We chose to use Vue directly to highlight some of the features that make it such a joy to work with. One of our favorite features is Vue’s single file components (SFC). We can include our JavaScript, HTML, and CSS for each component all in the same file. This makes it easier to keep all related code directly next to each other, making it easier to debug issues, and allowing less file flipping. Since we’re in Vue 3, we’re also able to make use of the new Composition API, which looks and feels a bit more like vanilla JavaScript. You can import files, create functions, and do most anything you could in regular JavaScript within your component’s script tag. Any variable name you create is automatically available within your HTML template. Provide and Inject Another feature we got to use specifically in this starter kit is the new provide and inject functionality. You can read more details about this in the Vue docs, but this feature gives us a way to avoid prop drilling and provide values directly where they’re needed. In this starter kit, we include a “greeting” example, which makes an API call using a provided message, and shows the user a generated greeting. Initially, we provided this message as a prop through the router to the greeting component. This works, but it did require us to do a little more legwork to provide a fallback value, as well as needing our router to be aware of the prop. Using the provide / inject setup, we’re able to provide our message through the root level of the app, making it globally available to any child component. Then, when we need to use it in our ` component, we inject the “key” we expect (our message), and it provides a built-in way for us to provide a default value to use as a fallback. Now our router doesn’t need to do any prop handling! And our component consistently works with the provided value or offers our default if something goes wrong. ` ` Using XState If you haven’t had a chance to look into XState before, we highly recommend checking out their documentation. They have a great intro to state machines and state charts that explains the concepts really well. One of the biggest mindset shifts that happens when you work with state machines is that they really help you think through how your application should work. State machines make you think explicitly through the different modes or “states” your application can get into, and what actions or side effects should happen in those states. By thinking directly through these, it helps you avoid sneaky edge cases and mutations you don’t expect. Difference between Context and State One of the parts that can be a little confusing at first is the difference between “state” and “context” when it comes to state machines. It can be easy to think of state as any values you store in your application that you want to persist between components or paths, and that can be accurate. However, with XState, a “state” is really more the idea of what configurations your app can be in. A common example is a music player. Your player can be in an “off” state, a “playing” state, or a “paused” state. These are all different modes, if you will, that can happen when your music player is interacted with. They can be values in a way, but they’re really more like the versions of your interface that you want to exist. You can transition between states, but when you go back to a specific state, you expect everything to behave the same way each time. States can trigger changes to your data or make API calls, but each time you enter or leave a state, you should be able to see the same actions occur. They give you stability and help prevent hidden edge cases. Values that we normally think of as state, things like strings or numbers or objects, that might change as your application is interacted with. These are the values that are stored in the “context” within XState. Our context values are the pieces of our application that are quantitative and that we expect will change as our application is working. ` Declaring Actions and Services When we create a state machine with XState, it accepts two values- a config object and an options object. The config tells us what the machine does. This is where we define our states and transitions. In the options object, we can provide more information on how the machine does things, including logic for guards, actions, and effects. You can write your actions and effect logic within the state that initiates those calls, which can be great for getting the machine working in the beginning. However, it’s recommended to make those into named functions within the options object, making it easier to debug issues and improving the readability for how our machine works. Cypress Testing The last interesting thing we’d like to talk about is our setup for using component testing in Cypress! To use their component testing feature, they provide you with a mount command, which handles mounting your individual components onto their test runner so you can unit test them in isolation. While this works great out of the box, there’s also a way to customize the mount command if you need to! This is where you’d want to add any configuration your application needs to work properly in a testing setup. Things like routing and state management setups would get added to this function. Since we made use of Vue’s provide and inject functions, we needed to add the provided value to our ` command in order for our greeting test to properly work. With that set up, we can allow it to provide our default empty string for tests that don’t need to worry about injecting a value (or when we specifically want to test our default value), and then we can inject the value we want in the tests that do need a specific value! ` Conclusion We hope you enjoy using this starter kit! We’ve touched a bit on the benefits of using Vue 3, how XState keeps our application working as we expect, and how we can test our components with Cypress. Have a request or a question about a [starter.dev] project? Reach out in the issues to make your requests or ask us your questions. The project is 100% open sourced so feel free to hop in and code with us!...

Jul 17, 2023

6 mins

VueXState

Next.js Rendering Strategies and how they affect core web vitals

When it comes to building fast and scalable web apps with Next.js, it’s important to understand how rendering works, especially with the App Router. Next.js organizes rendering around two main environments: the server and the client. On the server side, you’ll encounter three key strategies: Static Rendering, Dynamic Rendering, and Streaming. Each one comes with its own set of trade-offs and performance benefits, so knowing when to use which is crucial for delivering a great user experience. In this post, we'll break down each strategy, what it's good for, and how it impacts your site's performance, especially Core Web Vitals. We'll also explore hybrid approaches and provide practical guidance on choosing the right strategy for your use case. What Are Core Web Vitals? Core Web Vitals are a set of metrics defined by Google that measure real-world user experience on websites. These metrics play a major role in search engine rankings and directly affect how users perceive the speed and smoothness of your site. * Largest Contentful Paint (LCP): This measures loading performance. It calculates the time taken for the largest visible content element to render. A good LCP is 2.5 seconds or less. * Interaction to Next Paint (INP): This measures responsiveness to user input. A good INP is 200 milliseconds or less. * Cumulative Layout Shift (CLS): This measures the visual stability of the page. It quantifies layout instability during load. A good CLS is 0.1 or less. If you want to dive deeper into Core Web Vitals and understand more about their impact on your website's performance, I recommend reading this detailed guide on New Core Web Vitals and How They Work. Next.js Rendering Strategies and Core Web Vitals Let's explore each rendering strategy in detail: 1. Static Rendering (Server Rendering Strategy) Static Rendering is the default for Server Components in Next.js. With this approach, components are rendered at build time (or during revalidation), and the resulting HTML is reused for each request. This pre-rendering happens on the server, not in the user's browser. Static rendering is ideal for routes where the data is not personalized to the user, and this makes it suitable for: * Content-focused websites: Blogs, documentation, marketing pages * E-commerce product listings: When product details don't change frequently * SEO-critical pages: When search engine visibility is a priority * High-traffic pages: When you want to minimize server load How Static Rendering Affects Core Web Vitals * Largest Contentful Paint (LCP): Static rendering typically leads to excellent LCP scores (typically < 1s). The Pre-rendered HTML can be cached and delivered instantly from CDNs, resulting in very fast delivery of the initial content, including the largest element. Also, there is no waiting for data fetching or rendering on the client. * Interaction to Next Paint (INP): Static rendering provides a good foundation for INP, but doesn't guarantee optimal performance (typically ranges from 50-150 ms depending on implementation). While Server Components don't require hydration, any Client Components within the page still need JavaScript to become interactive. To achieve a very good INP score, you will need to make sure the Client Components within the page is minimal. * Cumulative Layout Shift (CLS): While static rendering delivers the complete page structure upfront which can be very beneficial for CLS, achieving excellent CLS requires additional optimization strategies: * Static HTML alone doesn't prevent layout shifts if resources load asynchronously * Image dimensions must be properly specified to reserve space before the image loads * Web fonts can cause text to reflow if not handled properly with font display strategies * Dynamically injected content (ads, embeds, lazy-loaded elements) can disrupt layout stability * CSS implementation significantly impacts CLS—immediate availability of styling information helps maintain visual stability Code Examples: 1. Basic static rendering: ` 2. Static rendering with revalidation (ISR): ` 3. Static path generation: ` 2. Dynamic Rendering (Server Rendering Strategy) Dynamic Rendering generates HTML on the server for each request at request time. Unlike static rendering, the content is not pre-rendered or cached but freshly generated for each user. This kind of rendering works best for: * Personalized content: User dashboards, account pages * Real-time data: Stock prices, live sports scores * Request-specific information: Pages that use cookies, headers, or search parameters * Frequently changing data: Content that needs to be up-to-date on every request How Dynamic Rendering Affects Core Web Vitals * Largest Contentful Paint (LCP): With dynamic rendering, the server needs to generate HTML for each request, and that can't be fully cached at the CDN level. It is still faster than client-side rendering as HTML is generated on the server. * Interaction to Next Paint (INP): The performance is similar to static rendering once the page is loaded. However, it can become slower if the dynamic content includes many Client Components. * Cumulative Layout Shift (CLS): Dynamic rendering can potentially introduce CLS if the data fetched at request time significantly alters the layout of the page compared to a static structure. However, if the layout is stable and the dynamic content size fits within predefined areas, the CLS can be managed effectively. Code Examples: 1. Explicit dynamic rendering: ` 2. Simplicit dynamic rendering with cookies: ` 3. Dynamic routes: ` 3. Streaming (Server Rendering Strategy) Streaming allows you to progressively render UI from the server. Instead of waiting for all the data to be ready before sending any HTML, the server sends chunks of HTML as they become available. This is implemented using React's Suspense boundary. React Suspense works by creating boundaries in your component tree that can "suspend" rendering while waiting for asynchronous operations. When a component inside a Suspense boundary throws a promise (which happens automatically with data fetching in React Server Components), React pauses rendering of that component and its children, renders the fallback UI specified in the Suspense component, continues rendering other parts of the page outside this boundary, and eventually resumes and replaces the fallback with the actual component once the promise resolves. When streaming, this mechanism allows the server to send the initial HTML with fallbacks for suspended components while continuing to process suspended components in the background. The server then streams additional HTML chunks as each suspended component resolves, including instructions for the browser to seamlessly replace fallbacks with final content. It works well for: * Pages with mixed data requirements: Some fast, some slow data sources * Improving perceived performance: Show users something quickly while slower parts load * Complex dashboards: Different widgets have different loading times * Handling slow APIs: Prevent slow third-party services from blocking the entire page How Streaming Affects Core Web Vitals * Largest Contentful Paint (LCP): Streaming can improve the perceived LCP. By sending the initial HTML content quickly, including potentially the largest element, the browser can render it sooner. Even if other parts of the page are still loading, the user sees the main content faster. * Interaction to Next Paint (INP): Streaming can contribute to a better INP. When used with React's <Suspense />, interactive elements in the faster-loading parts of the page can become interactive earlier, even while other components are still being streamed in. This allows users to engage with the page sooner. * Cumulative Layout Shift (CLS): Streaming can cause layout shifts as new content streams in. However, when implemented carefully, streaming should not negatively impact CLS. The initially streamed content should establish the main layout, and subsequent streamed chunks should ideally fit within this structure without causing significant reflows or layout shifts. Using placeholders and ensuring dimensions are known can help prevent CLS. Code Examples: 1. Basic Streaming with Suspense: ` 2. Nested Suspense boundaries for more granular control: ` 3. Using Next.js loading.js convention: ` 4. Client Components and Client-Side Rendering Client Components are defined using the React 'use client' directive. They are pre-rendered on the server but then hydrated on the client, enabling interactivity. This is different from pure client-side rendering (CSR), where rendering happens entirely in the browser. In the traditional sense of CSR (where the initial HTML is minimal, and all rendering happens in the browser), Next.js has moved away from this as a default approach but it can still be achievable by using dynamic imports and setting ssr: false. ` Despite the shift toward server rendering, there are valid use cases for CSR: 1. Private dashboards: Where SEO doesn't matter, and you want to reduce server load 2. Heavy interactive applications: Like data visualization tools or complex editors 3. Browser-only APIs: When you need access to browser-specific features like localStorage or WebGL 4. Third-party integrations: Some third-party widgets or libraries that only work in the browser While these are valid use cases, using Client Components is generally preferable to pure CSR in Next.js. Client Components give you the best of both worlds: server-rendered HTML for the initial load (improving SEO and LCP) with client-side interactivity after hydration. Pure CSR should be reserved for specific scenarios where server rendering is impossible or counterproductive. Client components are good for: * Interactive UI elements: Forms, dropdowns, modals, tabs * State-dependent UI: Components that change based on client state * Browser API access: Components that need localStorage, geolocation, etc. * Event-driven interactions: Click handlers, form submissions, animations * Real-time updates: Chat interfaces, live notifications How Client Components Affect Core Web Vitals * Largest Contentful Paint (LCP): Initial HTML includes the server-rendered version of Client Components, so LCP is reasonably fast. Hydration can delay interactivity but doesn't necessarily affect LCP. * Interaction to Next Paint (INP): For Client Components, hydration can cause input delay during page load, and when the page is hydrated, performance depends on the efficiency of event handlers. Also, complex state management can impact responsiveness. * Cumulative Layout Shift (CLS): Client-side data fetching can cause layout shifts as new data arrives. Also, state changes might alter the layout unexpectedly. Using Client Components will require careful implementation to prevent shifts. Code Examples: 1. Basic Client Component: ` 2. Client Component with server data: ` Hybrid Approaches and Composition Patterns In real-world applications, you'll often use a combination of rendering strategies to achieve the best performance. Next.js makes it easy to compose Server and Client Components together. Server Components with Islands of Interactivity One of the most effective patterns is to use Server Components for the majority of your UI and add Client Components only where interactivity is needed. This approach: 1. Minimizes JavaScript sent to the client 2. Provides excellent initial load performance 3. Maintains good interactivity where needed ` Partial Prerendering (Next.js 15) Next.js 15 introduced Partial Prerendering, a new hybrid rendering strategy that combines static and dynamic content in a single route. This allows you to: 1. Statically generate a shell of the page 2. Stream in dynamic, personalized content 3. Get the best of both static and dynamic rendering Note: At the time of this writing, Partial Prerendering is experimental and is not ready for production use. Read more ` Measuring Core Web Vitals in Next.js Understanding the impact of your rendering strategy choices requires measuring Core Web Vitals in real-world conditions. Here are some approaches: 1. Vercel Analytics If you deploy on Vercel, you can use Vercel Analytics to automatically track Core Web Vitals for your production site: ` 2. Web Vitals API You can manually track Core Web Vitals using the web-vitals library: ` 3. Lighthouse and PageSpeed Insights For development and testing, use: * Chrome DevTools Lighthouse tab * PageSpeed Insights * Chrome User Experience Report Making Practical Decisions: Which Rendering Strategy to Choose? Choosing the right rendering strategy depends on your specific requirements. Here's a decision framework: Choose Static Rendering when * Content is the same for all users * Data can be determined at build time * Page doesn't need frequent updates * SEO is critical * You want the best possible performance Choose Dynamic Rendering when * Content is personalized for each user * Data must be fresh on every request * You need access to request-time information * Content changes frequently Choose Streaming when * Page has a mix of fast and slow data requirements * You want to improve perceived performance * Some parts of the page depend on slow APIs * You want to prioritize showing critical UI first Choose Client Components when * UI needs to be interactive * Component relies on browser APIs * UI changes frequently based on user input * You need real-time updates Conclusion Next.js provides a powerful set of rendering strategies that allow you to optimize for both performance and user experience. By understanding how each strategy affects Core Web Vitals, you can make informed decisions about how to build your application. Remember that the best approach is often a hybrid one, combining different rendering strategies based on the specific requirements of each part of your application. Start with Server Components as your default, use Static Rendering where possible, and add Client Components only where interactivity is needed. By following these principles and measuring your Core Web Vitals, you can create Next.js applications that are fast, responsive, and provide an excellent user experience....

May 30, 2025

9 mins

NextJS

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