diff --git a/blog/2016/03/24/introducing-hot-reloading.html b/blog/2016/03/24/introducing-hot-reloading.html index 3b55a488527..39d83d6723e 100644 --- a/blog/2016/03/24/introducing-hot-reloading.html +++ b/blog/2016/03/24/introducing-hot-reloading.html @@ -1,4 +1,4 @@ -Introducing Hot Reloading – React Native | A framework for building native apps using React
React Nativenext

Recent Posts

Introducing Hot Reloading

March 24, 2016 by Martín Bigio

React Native's goal is to give you the best possible developer experience. A big part of it is the time it takes between you save a file and be able to see the changes. Our goal is to get this feedback loop to be under 1 second, even as your app grows.

We got close to this ideal via three main features:

  • Use JavaScript as the language doesn't have a long compilation cycle time.
  • Implement a tool called Packager that transforms es6/flow/jsx files into normal JavaScript that the VM can understand. It was designed as a server that keeps intermediate state in memory to enable fast incremental changes and uses multiple cores.
  • Build a feature called Live Reload that reloads the app on save.

At this point, the bottleneck for developers is no longer the time it takes to reload the app but losing the state of your app. A common scenario is to work on a feature that is multiple screens away from the launch screen. Every time you reload, you've got to click on the same path again and again to get back to your feature, making the cycle multiple-seconds long.

Hot Reloading #

The idea behind hot reloading is to keep the app running and to inject new versions of the files that you edited at runtime. This way, you don't lose any of your state which is especially useful if you are tweaking the UI.

A video is worth a thousand words. Check out the difference between Live Reload (current) and Hot Reload (new).

+Introducing Hot Reloading – React Native | A framework for building native apps using React
React Nativenext

Recent Posts

Introducing Hot Reloading

March 24, 2016 by Martín Bigio

React Native's goal is to give you the best possible developer experience. A big part of it is the time it takes between you save a file and be able to see the changes. Our goal is to get this feedback loop to be under 1 second, even as your app grows.

We got close to this ideal via three main features:

  • Use JavaScript as the language doesn't have a long compilation cycle time.
  • Implement a tool called Packager that transforms es6/flow/jsx files into normal JavaScript that the VM can understand. It was designed as a server that keeps intermediate state in memory to enable fast incremental changes and uses multiple cores.
  • Build a feature called Live Reload that reloads the app on save.

At this point, the bottleneck for developers is no longer the time it takes to reload the app but losing the state of your app. A common scenario is to work on a feature that is multiple screens away from the launch screen. Every time you reload, you've got to click on the same path again and again to get back to your feature, making the cycle multiple-seconds long.

Hot Reloading #

The idea behind hot reloading is to keep the app running and to inject new versions of the files that you edited at runtime. This way, you don't lose any of your state which is especially useful if you are tweaking the UI.

A video is worth a thousand words. Check out the difference between Live Reload (current) and Hot Reload (new).

If you look closely, you can notice that it is possible to recover from a red box and you can also start importing modules that were not previously there without having to do a full reload.

Word of warning: because JavaScript is a very stateful language, hot reloading cannot be perfectly implemented. In practice, we found out that the current setup is working well for a large amount of usual use cases and a full reload is always available in case something gets messed up.

Hot reloading is available as of 0.22, you can enable it:

  • Open the developer menu
  • Tap on "Enable Hot Reloading"

Implementation in a nutshell #

Now that we've seen why we want it and how to use it, the fun part begins: how it actually works.

Hot Reloading is built on top of a feature Hot Module Replacement, or HMR. It was first introduced by Webpack and we implemented it inside of React Native Packager. HMR makes the Packager watch for file changes and send HMR updates to a thin HMR runtime included on the app.

In a nutshell, the HMR update contains the new code of the JS modules that changed. When the runtime receives them, it replaces the old modules' code with the new one:

The HMR update contains a bit more than just the module's code we want to change because replacing it, it's not enough for the runtime to pick up the changes. The problem is that the module system may have already cached the exports of the module we want to update. For instance, say you have an app composed of these two modules:

// log.js function log(message) { diff --git a/blog/2016/07/06/toward-better-documentation.html b/blog/2016/07/06/toward-better-documentation.html index 66b6256428f..f39824480eb 100644 --- a/blog/2016/07/06/toward-better-documentation.html +++ b/blog/2016/07/06/toward-better-documentation.html @@ -1,4 +1,4 @@ -Toward Better Documentation – React Native | A framework for building native apps using React
React Nativenext

Recent Posts

Toward Better Documentation

July 6, 2016 by Kevin Lacker

Part of having a great developer experience is having great documentation. A lot goes into creating good docs - the ideal documentation is concise, helpful, accurate, complete, and delightful. Recently we've been working hard to make the docs better based on your feedback, and we wanted to share some of the improvements we've made.

Inline Examples #

When you learn a new library, a new programming language, or a new framework, there's a beautiful moment when you first write a bit of code, try it out, see if it works... and it does work. You created something real. We wanted to put that visceral experience right into our docs. Like this:

import React, { Component } from 'react'; +Toward Better Documentation – React Native | A framework for building native apps using React
React Nativenext

Recent Posts

Toward Better Documentation

July 6, 2016 by Kevin Lacker

Part of having a great developer experience is having great documentation. A lot goes into creating good docs - the ideal documentation is concise, helpful, accurate, complete, and delightful. Recently we've been working hard to make the docs better based on your feedback, and we wanted to share some of the improvements we've made.

Inline Examples #

When you learn a new library, a new programming language, or a new framework, there's a beautiful moment when you first write a bit of code, try it out, see if it works... and it does work. You created something real. We wanted to put that visceral experience right into our docs. Like this:

import React, { Component } from 'react'; import { AppRegistry, Text, View } from 'react-native'; class ScratchPad extends Component { diff --git a/blog/2016/08/12/react-native-meetup-san-francisco.html b/blog/2016/08/12/react-native-meetup-san-francisco.html new file mode 100644 index 00000000000..faf1f62d137 --- /dev/null +++ b/blog/2016/08/12/react-native-meetup-san-francisco.html @@ -0,0 +1,19 @@ +San Francisco Meetup Recap – React Native | A framework for building native apps using React
React Nativenext

Recent Posts

San Francisco Meetup Recap

August 12, 2016 by Héctor Ramos

Last week I had the opportunity to attend the React Native Meetup at Zynga’s San Francisco office. With around 200 people in attendance, it served as a great place to meet other developers near me that are also interested in React Native.

I was particularly interested in learning more about how React and React Native are used at companies like Zynga, Netflix, and Airbnb. The agenda for the night would be as follows:

  • Rapid Prototyping in React
  • Designing APIs for React Native
  • Bridging the Gap: Using React Native in Existing Codebases

But first, the event started off with a quick introduction and a brief recap of recent news:

If one of these meetups is held near you, I highly recommend attending!

Rapid Prototyping in React at Zynga #

The first round of news was followed by a quick introduction by Zynga, our hosts for the evening. Abhishek Chadha talked about how they use React to quickly prototype new experiences on mobile, demoing a quick prototype of a Draw Something-like app. They use a similar approach as React Native, providing access to native APIs via a bridge. This was demonstrated when Abhishek used the device's camera to snap a photo of the audience and then drew a hat on someone's head.

Designing APIs for React Native at Netflix #

Up next, the first featured talk of the evening. Clarence Leung, Senior Software Engineer at Netflix, presented his talk on Designing APIs for React Native. First he noted the two main types of libraries one may work on: components such as tab bars and date pickers, and libraries that provide access to native services such as the camera roll or in-app payments. There are two ways one may approach when building a library for use in React Native:

  • Provide platform-specific components
  • A cross-platform library with a similar API for both iOS and Android

Each approach has its own considerations, and it’s up to you to determine what works best for your needs.

Approach #1

As an example of platform-specific components, Clarence talked about the DatePickerIOS and DatePickerAndroid from core React Native. On iOS, date pickers are rendered as part of the UI and can be easily embedded in an existing view, while date pickers on Android are presented modally. It makes sense to provide separate components in this case.

Approach #2

Photo pickers, on the other hand, are treated similarly on iOS and Android. There are some slight differences — Android does not group photos into folders like iOS does with Selfies, for example — but those are easily handled using if statements and the Platform component.

Regardless of which approach you settle on, it’s a good idea to minimize the API surface and build app-specific libraries. For example, iOS’s In-App Purchase framework supports one-time, consumable purchases, as well as renewable subscriptions. If your app will only need to support consumable purchases, you may get away with dropping support for subscriptions in your cross-platform library.

There was a brief Q&A session at the end of Clarence’s talk. One of the interesting tid bits that came out of it was that around 80% of the React Native code written for these libraries at Netflix is shared across both iOS and Android.

Bridging the Gap, Using React Native in Existing Codebases #

The final talk of the night was by Leland Richardson from Airbnb. The talk was focused on the use of React Native in existing codebases. I already know how easy it is to write a new app from scratch using React Native, so I was very interested to hear about Airbnb’s experience adopting React Native in their existing native apps.

Leland started off by talking about greenfield apps versus brownfield apps. Greenfield means to start a project without the need to consider any prior work. This is in contrast to brownfield projects where you need to take into account the existing project’s requirements, development processes, and all of the teams various needs.

When you’re working on a greenfield app, the React Native CLI sets up a single repository for both iOS and Android and everything just works. The first challenge against using React Native at Airbnb was the fact that the iOS and Android app each had their own repository. Multi-repo companies have some hurdles to get past before they can adopt React Native.

To get around this, Airbnb first set up a new repo for the React Native codebase. They used their continuous integration servers to mirror the iOS and Android repos into this new repo. After tests are run and the bundle is built, the build artifacts are synced back to the iOS and Android repos. This allows the mobile engineers to work on native code without altering their development enviroment. Mobile engineers don't need to install npm, run the packager, or remember to build the JavaScript bundle. The engineers writing actual React Native code do not have to worry about syncing their code across iOS and Android, as they work on the React Native repository directly.

This does come with some drawbacks, mainly they could not ship atomic updates. Changes that require a combination of native and JavaScript code would require three separate pull requests, all of which had to be carefully landed. In order to avoid conflicts, CI will fail to land changes back to the iOS and Android repos if master has changed since the build started. This would cause long delays during high commit frequency days (such as when new releases are cut).

Airbnb has since moved to a mono repo approach. Fortunately this was already under consideration, and once the iOS and Android teams became comfortable with using React Native they were happy to accelerate the move towards the mono repo.

This has solved most of the issues they had with the split repo approach. Leland did note that this does cause a higher strain on the version control servers, which may be an issue for smaller companies.

The Navigation Problem #

The second half of Leland's talk focused on a topic that is dear to me: the Navigation problem in React Native. He talked about the abundance of navigation libraries in React Native, both first party and third party. NavigationExperimental was mentioned as something that seemed promising, but ended up not being well suited for their use case.

In fact, none of the existing navigation libraries seem to work well for brownfield apps. A brownfield app requires that the navigation state be fully owned by the native app. For example, if a user’s session expires while a React Native view is being presented, the native app should be able to take over and present a login screen as needed.

Airbnb also wanted to avoid replacing native navigation bars with JavaScript versions as part of a transition, as the effect could be jarring. Initially they limited themselves to modally presented views, but this obviously presented a problem when it came to adopting React Native more widely within their apps.

They decided that they needed their own library. The library is called airbnb-navigation. The library has not yet being open sourced as it is strongly tied to Airbnb’s codebase, but it is something they’d like to release by the end of the year.

I won’t go into much detail into the library’s API, but here are some of the key takeaways:

  • One must preregister scenes ahead of time
  • Each scene is displayed within its own RCTRootView. They are presented natively on each platform (e.g. UINavigationControllers are used on iOS).
  • The main ScrollView in a scene should be wrapped in a ScrollScene component. Doing so allows you to take advantage of native behaviors such as tapping on the status bar to scroll to the top on iOS.
  • Transitions between scenes are handled natively, no need to worry about performance.
  • The Android back button is automatically supported.
  • They can take advantage of View Controller based navigation bar styling via a Navigator.Config UI-less component.

There’s also some considerations to keep in mind:

  • The navigation bar is not easily customized in JavaScript, as it is a native component. This is intentional, as using native navigation bars is a hard requirement for this type of library.
  • ScreenProps must be serialized/de-serialized whenever they're sent through the bridge, so care must be taken if sending too much data here.
  • Navigation state is owned by the native app (also a hard requirement for the library), so things like Redux cannot manipulate navigation state.

Leland's talk was also followed by a Q&A session. Overall, Airbnb is satisfied with React Native. They’re interested in using Code Push to fix any issues without going through the App Store, and their engineers love Live Reload, as they don't have to wait for the native app to be rebuilt after every minor change.

Closing Remarks #

The event ended with some additional React Native news:

Meetups provide a good opportunity to meet and learn from other developers in the community. I'm looking forward to attending more React Native meetups in the future. If you make it up to one of these, please look out for me and let me know how we can make React Native work better for you!

© 2016 Facebook Inc.
\ No newline at end of file diff --git a/blog/img/rnmsf-august-2016-airbnb.jpg b/blog/img/rnmsf-august-2016-airbnb.jpg new file mode 100644 index 00000000000..bbbc28957fb Binary files /dev/null and b/blog/img/rnmsf-august-2016-airbnb.jpg differ diff --git a/blog/img/rnmsf-august-2016-docs.jpg b/blog/img/rnmsf-august-2016-docs.jpg new file mode 100644 index 00000000000..a89b25fc26e Binary files /dev/null and b/blog/img/rnmsf-august-2016-docs.jpg differ diff --git a/blog/img/rnmsf-august-2016-hero.jpg b/blog/img/rnmsf-august-2016-hero.jpg new file mode 100644 index 00000000000..35479f3584f Binary files /dev/null and b/blog/img/rnmsf-august-2016-hero.jpg differ diff --git a/blog/img/rnmsf-august-2016-netflix.jpg b/blog/img/rnmsf-august-2016-netflix.jpg new file mode 100644 index 00000000000..2ee4f0d8deb Binary files /dev/null and b/blog/img/rnmsf-august-2016-netflix.jpg differ diff --git a/blog/index.html b/blog/index.html index 1f3fd8727e2..37a8db9231e 100644 --- a/blog/index.html +++ b/blog/index.html @@ -1,4 +1,4 @@ -Blog – React Native | A framework for building native apps using React
React Nativenext

Recent Posts

Toward Better Documentation

July 6, 2016 by Kevin Lacker

Part of having a great developer experience is having great documentation. A lot goes into creating good docs - the ideal documentation is concise, helpful, accurate, complete, and delightful. Recently we've been working hard to make the docs better based on your feedback, and we wanted to share some of the improvements we've made.

Inline Examples #

When you learn a new library, a new programming language, or a new framework, there's a beautiful moment when you first write a bit of code, try it out, see if it works... and it does work. You created something real. We wanted to put that visceral experience right into our docs. Like this:

import React, { Component } from 'react'; +Blog – React Native | A framework for building native apps using React
React Nativenext

Recent Posts

San Francisco Meetup Recap

August 12, 2016 by Héctor Ramos

Last week I had the opportunity to attend the React Native Meetup at Zynga’s San Francisco office. With around 200 people in attendance, it served as a great place to meet other developers near me that are also interested in React Native.

I was particularly interested in learning more about how React and React Native are used at companies like Zynga, Netflix, and Airbnb. The agenda for the night would be as follows:

  • Rapid Prototyping in React
  • Designing APIs for React Native
  • Bridging the Gap: Using React Native in Existing Codebases

But first, the event started off with a quick introduction and a brief recap of recent news:

If one of these meetups is held near you, I highly recommend attending!

Rapid Prototyping in React at Zynga #

The first round of news was followed by a quick introduction by Zynga, our hosts for the evening. Abhishek Chadha talked about how they use React to quickly prototype new experiences on mobile, demoing a quick prototype of a Draw Something-like app. They use a similar approach as React Native, providing access to native APIs via a bridge. This was demonstrated when Abhishek used the device's camera to snap a photo of the audience and then drew a hat on someone's head.

Designing APIs for React Native at Netflix #

Up next, the first featured talk of the evening. Clarence Leung, Senior Software Engineer at Netflix, presented his talk on Designing APIs for React Native. First he noted the two main types of libraries one may work on: components such as tab bars and date pickers, and libraries that provide access to native services such as the camera roll or in-app payments. There are two ways one may approach when building a library for use in React Native:

  • Provide platform-specific components
  • A cross-platform library with a similar API for both iOS and Android

Each approach has its own considerations, and it’s up to you to determine what works best for your needs.

Approach #1

As an example of platform-specific components, Clarence talked about the DatePickerIOS and DatePickerAndroid from core React Native. On iOS, date pickers are rendered as part of the UI and can be easily embedded in an existing view, while date pickers on Android are presented modally. It makes sense to provide separate components in this case.

Approach #2

Photo pickers, on the other hand, are treated similarly on iOS and Android. There are some slight differences — Android does not group photos into folders like iOS does with Selfies, for example — but those are easily handled using if statements and the Platform component.

Regardless of which approach you settle on, it’s a good idea to minimize the API surface and build app-specific libraries. For example, iOS’s In-App Purchase framework supports one-time, consumable purchases, as well as renewable subscriptions. If your app will only need to support consumable purchases, you may get away with dropping support for subscriptions in your cross-platform library.

There was a brief Q&A session at the end of Clarence’s talk. One of the interesting tid bits that came out of it was that around 80% of the React Native code written for these libraries at Netflix is shared across both iOS and Android.

Bridging the Gap, Using React Native in Existing Codebases #

The final talk of the night was by Leland Richardson from Airbnb. The talk was focused on the use of React Native in existing codebases. I already know how easy it is to write a new app from scratch using React Native, so I was very interested to hear about Airbnb’s experience adopting React Native in their existing native apps.

Leland started off by talking about greenfield apps versus brownfield apps. Greenfield means to start a project without the need to consider any prior work. This is in contrast to brownfield projects where you need to take into account the existing project’s requirements, development processes, and all of the teams various needs.

When you’re working on a greenfield app, the React Native CLI sets up a single repository for both iOS and Android and everything just works. The first challenge against using React Native at Airbnb was the fact that the iOS and Android app each had their own repository. Multi-repo companies have some hurdles to get past before they can adopt React Native.

To get around this, Airbnb first set up a new repo for the React Native codebase. They used their continuous integration servers to mirror the iOS and Android repos into this new repo. After tests are run and the bundle is built, the build artifacts are synced back to the iOS and Android repos. This allows the mobile engineers to work on native code without altering their development enviroment. Mobile engineers don't need to install npm, run the packager, or remember to build the JavaScript bundle. The engineers writing actual React Native code do not have to worry about syncing their code across iOS and Android, as they work on the React Native repository directly.

This does come with some drawbacks, mainly they could not ship atomic updates. Changes that require a combination of native and JavaScript code would require three separate pull requests, all of which had to be carefully landed. In order to avoid conflicts, CI will fail to land changes back to the iOS and Android repos if master has changed since the build started. This would cause long delays during high commit frequency days (such as when new releases are cut).

Airbnb has since moved to a mono repo approach. Fortunately this was already under consideration, and once the iOS and Android teams became comfortable with using React Native they were happy to accelerate the move towards the mono repo.

This has solved most of the issues they had with the split repo approach. Leland did note that this does cause a higher strain on the version control servers, which may be an issue for smaller companies.

The Navigation Problem #

The second half of Leland's talk focused on a topic that is dear to me: the Navigation problem in React Native. He talked about the abundance of navigation libraries in React Native, both first party and third party. NavigationExperimental was mentioned as something that seemed promising, but ended up not being well suited for their use case.

In fact, none of the existing navigation libraries seem to work well for brownfield apps. A brownfield app requires that the navigation state be fully owned by the native app. For example, if a user’s session expires while a React Native view is being presented, the native app should be able to take over and present a login screen as needed.

Airbnb also wanted to avoid replacing native navigation bars with JavaScript versions as part of a transition, as the effect could be jarring. Initially they limited themselves to modally presented views, but this obviously presented a problem when it came to adopting React Native more widely within their apps.

They decided that they needed their own library. The library is called airbnb-navigation. The library has not yet being open sourced as it is strongly tied to Airbnb’s codebase, but it is something they’d like to release by the end of the year.

I won’t go into much detail into the library’s API, but here are some of the key takeaways:

  • One must preregister scenes ahead of time
  • Each scene is displayed within its own RCTRootView. They are presented natively on each platform (e.g. UINavigationControllers are used on iOS).
  • The main ScrollView in a scene should be wrapped in a ScrollScene component. Doing so allows you to take advantage of native behaviors such as tapping on the status bar to scroll to the top on iOS.
  • Transitions between scenes are handled natively, no need to worry about performance.
  • The Android back button is automatically supported.
  • They can take advantage of View Controller based navigation bar styling via a Navigator.Config UI-less component.

There’s also some considerations to keep in mind:

  • The navigation bar is not easily customized in JavaScript, as it is a native component. This is intentional, as using native navigation bars is a hard requirement for this type of library.
  • ScreenProps must be serialized/de-serialized whenever they're sent through the bridge, so care must be taken if sending too much data here.
  • Navigation state is owned by the native app (also a hard requirement for the library), so things like Redux cannot manipulate navigation state.

Leland's talk was also followed by a Q&A session. Overall, Airbnb is satisfied with React Native. They’re interested in using Code Push to fix any issues without going through the App Store, and their engineers love Live Reload, as they don't have to wait for the native app to be rebuilt after every minor change.

Closing Remarks #

The event ended with some additional React Native news:

Meetups provide a good opportunity to meet and learn from other developers in the community. I'm looking forward to attending more React Native meetups in the future. If you make it up to one of these, please look out for me and let me know how we can make React Native work better for you!

Toward Better Documentation

July 6, 2016 by Kevin Lacker

Part of having a great developer experience is having great documentation. A lot goes into creating good docs - the ideal documentation is concise, helpful, accurate, complete, and delightful. Recently we've been working hard to make the docs better based on your feedback, and we wanted to share some of the improvements we've made.

Inline Examples #

When you learn a new library, a new programming language, or a new framework, there's a beautiful moment when you first write a bit of code, try it out, see if it works... and it does work. You created something real. We wanted to put that visceral experience right into our docs. Like this:

import React, { Component } from 'react'; import { AppRegistry, Text, View } from 'react-native'; class ScratchPad extends Component { @@ -16,7 +16,7 @@ class ScratchPad extends } } -AppRegistry.registerComponent('ScratchPad', () => ScratchPad);

We think these inline examples, using the react-native-web-player module with help from Devin Abbott, are a great way to learn the basics of React Native, and we have updated our tutorial for new React Native developers to use these wherever possible. Check it out - if you have ever been curious to see what would happen if you modified just one little bit of sample code, this is a really nice way to poke around. Also, if you're building developer tools and you want to show a live React Native sample on your own site, react-native-web-player can make that straightforward.

The core simulation engine is provided by Nicolas Gallagher's react-native-web project, which provides a way to display React Native components like Text and View on the web. Check out react-native-web if you're interested in building mobile and web experiences that share a large chunk of the codebase.

Better Guides #

In some parts of React Native, there are multiple ways to do things, and we've heard feedback that we could provide better guidance.

We have a new guide to Navigation that compares the different approaches and advises on what you should use - Navigator, NavigatorIOS, NavigationExperimental. In the medium term, we're working towards improving and consolidating those interfaces. In the short term, we hope that a better guide will make your life easier.

We also have a new guide to handling touches that explains some of the basics of making button-like interfaces, and a brief summary of the different ways to handle touch events.

Another area we worked on is Flexbox. This includes tutorials on how to handle layout with Flexbox and how to control the size of components. It also includes an unsexy but hopefully-useful list of all the props that control layout in React Native.

Getting Started #

When you start getting a React Native development environment set up on your machine, you do have to do a bunch of installing and configuring things. It's hard to make installation a really fun and exciting experience, but we can at least make it as quick and painless as possible.

We built a new Getting Started workflow that lets you select your development operating system and your mobile operating system up front, to provide one concise place with all the setup instructions. We also went through the installation process to make sure everything worked and to make sure that every decision point had a clear recommendation. After testing it out on our innocent coworkers, we're pretty sure this is an improvement.

We also worked on the guide to integrating React Native into an existing app. Many of the largest apps that use React Native, like the Facebook app itself, actually build part of the app in React Native, and part of it using regular development tools. We hope this guide makes it easier for more people to build apps this way.

We Need Your Help #

Your feedback lets us know what we should prioritize. I know some people will read this blog post and think "Better docs? Pffft. The documentation for X is still garbage!". That's great - we need that energy. The best way to give us feedback depends on the sort of feedback.

If you find a mistake in the documentation, like inaccurate descriptions or code that doesn't actually work, file an issue. Tag it with "Documentation", so that it's easier to route it to the right people.

If there isn't a specific mistake, but something in the documentation is fundamentally confusing, it's not a great fit for a GitHub issue. Instead, complain on Product Pains about the area of the docs that could use help. This helps us prioritize when we are doing more general work like guide-writing.

Thanks for reading this far, and thanks for using React Native!

Introducing Hot Reloading

March 24, 2016 by Martín Bigio

React Native's goal is to give you the best possible developer experience. A big part of it is the time it takes between you save a file and be able to see the changes. Our goal is to get this feedback loop to be under 1 second, even as your app grows.

We got close to this ideal via three main features:

  • Use JavaScript as the language doesn't have a long compilation cycle time.
  • Implement a tool called Packager that transforms es6/flow/jsx files into normal JavaScript that the VM can understand. It was designed as a server that keeps intermediate state in memory to enable fast incremental changes and uses multiple cores.
  • Build a feature called Live Reload that reloads the app on save.

At this point, the bottleneck for developers is no longer the time it takes to reload the app but losing the state of your app. A common scenario is to work on a feature that is multiple screens away from the launch screen. Every time you reload, you've got to click on the same path again and again to get back to your feature, making the cycle multiple-seconds long.

Hot Reloading #

The idea behind hot reloading is to keep the app running and to inject new versions of the files that you edited at runtime. This way, you don't lose any of your state which is especially useful if you are tweaking the UI.

A video is worth a thousand words. Check out the difference between Live Reload (current) and Hot Reload (new).

+AppRegistry.registerComponent('ScratchPad', () => ScratchPad);

We think these inline examples, using the react-native-web-player module with help from Devin Abbott, are a great way to learn the basics of React Native, and we have updated our tutorial for new React Native developers to use these wherever possible. Check it out - if you have ever been curious to see what would happen if you modified just one little bit of sample code, this is a really nice way to poke around. Also, if you're building developer tools and you want to show a live React Native sample on your own site, react-native-web-player can make that straightforward.

The core simulation engine is provided by Nicolas Gallagher's react-native-web project, which provides a way to display React Native components like Text and View on the web. Check out react-native-web if you're interested in building mobile and web experiences that share a large chunk of the codebase.

Better Guides #

In some parts of React Native, there are multiple ways to do things, and we've heard feedback that we could provide better guidance.

We have a new guide to Navigation that compares the different approaches and advises on what you should use - Navigator, NavigatorIOS, NavigationExperimental. In the medium term, we're working towards improving and consolidating those interfaces. In the short term, we hope that a better guide will make your life easier.

We also have a new guide to handling touches that explains some of the basics of making button-like interfaces, and a brief summary of the different ways to handle touch events.

Another area we worked on is Flexbox. This includes tutorials on how to handle layout with Flexbox and how to control the size of components. It also includes an unsexy but hopefully-useful list of all the props that control layout in React Native.

Getting Started #

When you start getting a React Native development environment set up on your machine, you do have to do a bunch of installing and configuring things. It's hard to make installation a really fun and exciting experience, but we can at least make it as quick and painless as possible.

We built a new Getting Started workflow that lets you select your development operating system and your mobile operating system up front, to provide one concise place with all the setup instructions. We also went through the installation process to make sure everything worked and to make sure that every decision point had a clear recommendation. After testing it out on our innocent coworkers, we're pretty sure this is an improvement.

We also worked on the guide to integrating React Native into an existing app. Many of the largest apps that use React Native, like the Facebook app itself, actually build part of the app in React Native, and part of it using regular development tools. We hope this guide makes it easier for more people to build apps this way.

We Need Your Help #

Your feedback lets us know what we should prioritize. I know some people will read this blog post and think "Better docs? Pffft. The documentation for X is still garbage!". That's great - we need that energy. The best way to give us feedback depends on the sort of feedback.

If you find a mistake in the documentation, like inaccurate descriptions or code that doesn't actually work, file an issue. Tag it with "Documentation", so that it's easier to route it to the right people.

If there isn't a specific mistake, but something in the documentation is fundamentally confusing, it's not a great fit for a GitHub issue. Instead, complain on Product Pains about the area of the docs that could use help. This helps us prioritize when we are doing more general work like guide-writing.

Thanks for reading this far, and thanks for using React Native!

Introducing Hot Reloading

March 24, 2016 by Martín Bigio

React Native's goal is to give you the best possible developer experience. A big part of it is the time it takes between you save a file and be able to see the changes. Our goal is to get this feedback loop to be under 1 second, even as your app grows.

We got close to this ideal via three main features:

  • Use JavaScript as the language doesn't have a long compilation cycle time.
  • Implement a tool called Packager that transforms es6/flow/jsx files into normal JavaScript that the VM can understand. It was designed as a server that keeps intermediate state in memory to enable fast incremental changes and uses multiple cores.
  • Build a feature called Live Reload that reloads the app on save.

At this point, the bottleneck for developers is no longer the time it takes to reload the app but losing the state of your app. A common scenario is to work on a feature that is multiple screens away from the launch screen. Every time you reload, you've got to click on the same path again and again to get back to your feature, making the cycle multiple-seconds long.

Hot Reloading #

The idea behind hot reloading is to keep the app running and to inject new versions of the files that you edited at runtime. This way, you don't lose any of your state which is especially useful if you are tweaking the UI.

A video is worth a thousand words. Check out the difference between Live Reload (current) and Hot Reload (new).

If you look closely, you can notice that it is possible to recover from a red box and you can also start importing modules that were not previously there without having to do a full reload.

Word of warning: because JavaScript is a very stateful language, hot reloading cannot be perfectly implemented. In practice, we found out that the current setup is working well for a large amount of usual use cases and a full reload is always available in case something gets messed up.

Hot reloading is available as of 0.22, you can enable it:

  • Open the developer menu
  • Tap on "Enable Hot Reloading"

Implementation in a nutshell #

Now that we've seen why we want it and how to use it, the fun part begins: how it actually works.

Hot Reloading is built on top of a feature Hot Module Replacement, or HMR. It was first introduced by Webpack and we implemented it inside of React Native Packager. HMR makes the Packager watch for file changes and send HMR updates to a thin HMR runtime included on the app.

In a nutshell, the HMR update contains the new code of the JS modules that changed. When the runtime receives them, it replaces the old modules' code with the new one:

The HMR update contains a bit more than just the module's code we want to change because replacing it, it's not enough for the runtime to pick up the changes. The problem is that the module system may have already cached the exports of the module we want to update. For instance, say you have an app composed of these two modules:

// log.js function log(message) { diff --git a/releases/next/css/react-native.css b/releases/next/css/react-native.css index cd7ffe88799..4a9f952c034 100644 --- a/releases/next/css/react-native.css +++ b/releases/next/css/react-native.css @@ -1646,3 +1646,9 @@ input#algolia-doc-search:focus { .web-player.mobile > .prism { display: block; } + +/** Blog **/ + +.article { + margin: 0 0 40px 0; +}