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Classes from migrating a mountainous codebase to React 16

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Fb launched a rewrite of a mountainous share of React final week. React 16 has been powerful anticipated, and the new Fiber rendering pipeline permits for quite so much of performance enhancements. Whereas the React team has diligently deprecated techniques and packages at some level of the final version, warning us strongly in console statements to upgrade, the true closing migration is no longer trivial for bigger codebases. We at Discord fair launched our React 16 primarily primarily based mostly app and wished to allotment our expertise and some pointers we learned along the methodology.

Why fabricate it?

The architectural route of Fiber seems prefer it would possibly maybe maybe in the end be a magnificent smoother person expertise for both DOM and Native renderers by chunking up the render and prioritizing sooner bits first. Magnificent now, it isn’t certain that the advantages are most valuable (for one, asynchronous rendering is no longer enabled yet), nonetheless the adjustments pave the direction for such gains in the end.

Chances are you’ll perhaps very neatly be going to are looking out for to upgrade in the end. React is restful in glide, and to defend within the back of will absolutely leave you fixing against bugs long abandoned by the 16+ team. Additionally, the new ErrorBoundary is a welcome boost. There are quite so much of adjustments, and likewise you would possibly maybe perhaps must adapt.

The stage of effort

Cherish every migrations, the stage of effort would perhaps be straight correlated to how fresh most of your codebase is. Fb has carried out a fair job of deprecating and warning for the final few months, nonetheless no longer all libraries are neatly-maintained and whenever you happen to depend on or comprise forked a colossal many elderly ones, you would possibly maybe perhaps be in for rather of a slog.

Additionally it is a long way up to you and your team whether or no longer right here is the time to in the end transfer to ES6 classes in every single location, or realistic parts, or what comprise you ever. We strongly counsel doing that after you efficiently migrate, so that you would possibly maybe perhaps maybe also imprint what is breaking (and ideally covering with assessments) sooner than making it fantastically trendy. Additionally, you would possibly maybe perhaps are looking out for to identify that migration as rapid as that you would possibly maybe perhaps maybe also bring to mind so that you would possibly maybe perhaps maybe also rapid launch trying out after which deploying your branch. Having this sit out on a PR for about a weeks will enable grasp to transfer previous you to the level that you would possibly maybe perhaps must fabricate all of it all over again.

We had been starting with a fair positive codebase, nonetheless one that is tall adequate to comprise no longer migrated off of mixins and React.createClass within the massive majority of parts. We also pin to mumble bundle versions, which methodology we’re earn and warranted, nonetheless our dependencies can change into ragged and mossy.

Here is the keep the bother came.

Bustle the codemod

First and predominant, you would possibly maybe perhaps maybe also restful spend the Fb codemod to transfer from React.PropTypes to prop-sorts, and to migrate off of React.createClass. The codemod will originate rather shimmering choices, exciting you to a class if that you would possibly maybe perhaps maybe also bring to mind (and a PureComponent class whenever you happen to spend the pure mixin), or shimming it with originate-react-class.

Install jscodeshift, after which clone the react-codemod repo. Then flee the next against your codebase:

  • Circulate to prop-sorts bundle:
jscodeshift -t ./react-codemod/transforms/React-PropTypes-to-prop-sorts.js /direction/to/your/repo
  • Circulate to Ingredient, PureComponent, or createReactClass:

jscodeshift -t ./react-codemod/transforms/class.js --mixin-module-name=react-addons-pure-render-mixin --proceed along with the glide=fair --pure-ingredient=fair --engage away-runtime-proptypes=erroneous /direction/to/your/repo

The latter is doing quite so much of issues, neatly described on the github page. Most importantly:

  • Moves to an ES6 class if no mixins, and PureComponent if top likely the pure mixin is original.
  • If a class is created, all static are migrated.
  • Creates proceed along with the glide annotations from propTypes.
  • Migrates capacity binding from constructor to arrow capabilities, whenever you happen to love that fabricate of ingredient.
  • Skips any ingredient utilizing deprecated APIs like isMounted() and many others.

The codemod chanced on a need of errors in our codebase, which you would possibly maybe perhaps maybe also restful tag after which fight through and steady by hand.

If you fabricate no longer like their codemod, or choices, you would possibly maybe perhaps maybe also restful absolutely modify it to your taste or write your occupy. The codemod is an fair true-looking out instrument, nonetheless no longer a magic wand. This alone will no longer migrate you!

Search and exchange

We chanced on that we had to search and exchange a need of spots the keep the the codemod skipped over it. Spots the keep we had imported PropTypes from React and known as it straight, likely. The top likely manual adjustment for us used to be hunting down all of the isMounted() calls and as a exchange making a property _isMounted which is determined to fair interior componentDidMount, and erroneous interior componentWillUnmount (though perhaps you shouldn’t).

Changing interior most API utilization

Completely you don’t spend interior most APIs from interior React? The ones from react/lib/*. If you fabricate, the devs at Fb fabricate no longer comprise any pity for you: they comprise bricked you out of these.

About a of these were moved to external libraries (the ‘react-addons-’ household of packages) nonetheless in some conditions, they are fair long previous.

Our code has a custom TransitionGroup which relied on the flattenChildren feature from interior react/lib. However this feature is now long previous, as are the related childMapping and mergeChildMappings capabilities. React devs counsel “inlining” (ie, reproduction-and-pasting) the dear capabilities, which is what we in the end did. Nonetheless, we inlined the newer versions of these capabilities from interior react-transition.

Discovering this disclose, and resolving it, used to be the most valuable tall hurdle, nonetheless our app restful did no longer yet flee.

Upgrading dependencies

This one is leisurely, and whenever you happen to are no longer in a bustle to get on 16 is probably going to be price ready till extra libraries check and upgrade themselves. If you defend to aid in that assignment, on the choice hand, this can aid everyone.

The console will defend warning you about packages that call React.PropTypes or spend React.createClass. You’re going to must upgrade these if that you would possibly maybe perhaps maybe also bring to mind, exchange or work around them if valuable, or fork and fix them if the bundle seems to be unmaintained.

The principle points you are having a analysis to resolve for are:

  1. Uses React.PropTypes
  2. Uses React.createClass
  3. Relies upon straight on pre-React 16 internals

Quantity 3 will consequence in an error about ref possession, and there being better than one React bundle. Search your account.lock for who’s depending straight on React < 16 (they also can restful be utilizing a look dependency!), and upgrade these first.

However no longer all bundle errors are so with out complications chanced on, and herein lies the staunch effort.

We bumped into an error which took us 2 days to note down to a library, and likewise you would possibly maybe perhaps maybe also obtain the same. The console saved telling us that reactFiberChild would possibly maybe perhaps maybe now not render an ingredient on myth of its ref used to be undefined. We tore our hair out puzzling through how this would possibly maybe perhaps happen, and in the end dug into the React code and noticed the keep the error used to be being generated. React 16 doesn’t like undefined ref attributes, nonetheless null are fair true-looking out. It took us some time to look for that aspects created with a core external library had been being keep with ref: undefined. When we forked and fastened it, the entirety rendered fantastically.

Delicate surprises

Neatly, we also chanced on that there were subtle errors right here and there at some level of the code, all all over again mostly these which required exciting through dependent libraries and upgrading or fixing them. Typically upgrading a library that is rather ragged will alter its rendering, blowing out your carefully crafted CSS overrides. Since most libraries comprise top likely fastened their points once the deprecation warnings showed up in React 15.5+, top likely their most modern version will work. Here is leisurely work to look for and fix.

Keen to ES6 classes for React 16 methodology that you now must be fastidious about no longer altering props. Where you previously got a warning about this, now it fails arduous with a “Can no longer place to learn top likely property XXX of object ‘#’”. If you destructure props, and engage a analysis at to alter these properties (or properties on these objects), this also can bite you. As an alternative place a brand new object with the updated price:

const newProp = {...prop, propertyToOverride: overrideValue}

Additionally, React 16 will warn about getting a boolean onClick price, which will happen whenever you happen to fabricate onClick={!disabled && this.handleOnClick}. Handle the disabled affirm within the feature to resolve.

And then there would possibly maybe be React Native

We even comprise an iOS app which shares stores, utils, and some action creators with the win app. Migrating to React 16 used to be in rather a lot of ways motivated by our heavy spend of React Native, as newer RN releases depend on the alphas of React 16.

Sadly, on myth of we need some special timers for video, we have a fork of React Native and were back on zero.34. React 16 compatibility top likely arrived in RN in zero.Forty eight.zero, so it is time to migrate…

We chanced on this to be especially painful. The top likely headache used to be that we frail React Native Webpack Server so as to reuse code between our projects, and this mission used to be abandoned a year within the past (very arduous to constantly shadow the RN codebase). So we wished to are looking forward to at our make tooling, and began to migrate to Haul.

Haul keeps us within the webpack universe, nonetheless used to be no longer trivial to setup in an existing codebase. That can perhaps maybe likely be the field of 1 other publish.

Additionally, we have been importing iOS images utilizing the webpack-y require(‘image!image_src’), which used to be now no longer that you would possibly maybe perhaps maybe also bring to mind in newer versions of RN. This used to be grueling work, since we had to transfer the image resources and trade how we accessed them (by importing the images straight and referencing the import). Even after writing a codemod, this used to be mostly manual.

The relaxation of the React Native migration used to be executed by making a record of breaking adjustments from all of the intermediate RN trade logs, and going through them one after the other. As an illustration, the behavior of flex styling used to be (wisely) modified, and as a consequence our utilization needed to be adjusted at some level of the app. This used to be painstaking, nonetheless the most productive direction.

You’re going to also obtain many classes were deprecated. For now, we counsel you spend the shim react-native-deprecated-custom-parts. Chances are you’ll perhaps need the most up-to-date commit, since they top likely fair no longer too long within the past updated it for React 16.

Declare back of new parts

The top likely bit for us used to be the new ErrorBoundary. Since React 16 now aborts the render tree on an uncaught error (which is a fair ingredient), you’ll are looking out for to keep one thing to render to the person when this occurs. Additionally, the boundaries present a colossal opportunity to comprise a central keep for logging files-rich errors with both stack and ingredient traces.

It runs!

So now it renders, and your person expertise is fleshy of wonder and enjoyment. No? We chanced on it to be no sooner than React 15, nonetheless demand this to trade as we and the core devs pursue the advantages inherent within the new architecture.

The top likely back, like most tech debt funds, will come down the avenue. Our code has now been forcibly brought up to this level, and this allowed us to normalize powerful of the code vogue en passant while reconsidering one of the core tooling for instant or subsequent modernization. Performance is a bonus.

We are hiring, so come join us if this fabricate of stuff tickles your esteem.

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