Miłosz Orzeł

.net, js, html, arduino, java... no rants or clickbaits.

Notes from migrating React app from CRA to Vite


I've recently made the decision to migrate my vim.morzel.net pet-project from Create React App to Vite. To be honest, I was quite content with how CRA (with a bit of React App Rewired) functioned, and updating might not have been necessary. However, I wanted to use this migration as practice before possibly employing Vite on something more serious (where the speed and active development of Vite might prove a blessing).

Here's a summary of the front-end part of vim.morzel.net as reported by cloc on src directory:

Language                     files          blank        comment           code
TypeScript                      94            535             88           3382
CSS                             32            268             10           1613
JavaScript                       3             71             26            364
Markdown                         1             28              0             58
JSON                             1              0              0             15
SVG                              1              0              0              1
SUM:                           133            902            124           5433

The project is done mostly with TypeScript and CSS (modules). JS lines come primarily from glue code for WebAssembly module for drills (which is done in Rust in separate repository).

Most notable dependencies are Redux (with Toolkit), React Syntax Highlighter, Fontsource and React Testing Library. Full list with links is at the bottom of this page.

As you can see, the project is small, but nonetheless useful as a testing ground for migration to Vite.

Application is deployed on DigitalOcean droplet with Ubuntu 20.04, NGINX 1.18.0, Node.js 17.3.0 and PM2 5.10.

In this post I'll note my approach for the migration (which worked quite well) and the issues I ran into. Hopefully you will find some useful information here in case you plan to switch to Vite too.



Switching dev/build tooling sounded like a good occasion to upgrade the React version too (from 16.9.0 to 18.2.0). This went surprisingly smoothly, I just needed to update to new application root (details here).
Once on latest React, I went for newest Jest and React Testing Library without any blockers (wasn't sure yet about trying Vitest).



Initially the plan was to replace CRA features with Vite as described in this article or this one, but then I thought that I'm too much of a noob in Vite and I would rather start with a nice and clean Vite project and move the screens to that fresh setup. So I've created a branch for the Vite version and put there only the results of running Vite scaffolding (v4.3.9) for React with TypeScript and SWC. Then I checked out the CRA version (master branch) to another folder so I could easily move files around and have the two applications running side by side for comparison. Putting content from old version to the new was quite easy: basically copy & paste of folders with features, utils and overall app setup (like Redux store). Then copy some style and config files, favicon etc. A bit more attention was needed for putting chunks of code in index.html, src/main.tsx and src/App.tsx. I of course had to install a couple of dependencies that the app needed but were not part of Vite scaffolding...



There were a couple of things that required adjustments, here they are in random order - I might have forgot some, sorry :)

Port configuration

By default Vite runs dev server on port 5173, CRA does it on 3000. Since I had a couple of bookmarks with :3000 I wanted to keep it. It's easy to change: just add this to your vite.config.ts:

server: {
  port: 3000,
  open: true

The open flag will automatically launch browser when server starts (just like CRA does by default).

You can also add a config for running production build locally with npm run preview (no need for installing serve like in CRA):

preview: {
  port: 3000,
  open: true

Accessing config from .env files

The CRA version used .env files (like .env.development or .env.production) with the help of env-cmd package. Chosen values (prefixed with REACT_APP_) were automatically included in UI and accessed like this: process.env.REACT_APP_SOMETHING in code. Fortunately Vite has built-in support for .env files (thanks to dotenv), but exposed values should be prefixed with VITE_. Access to values is slightly different, there is no process.env but you should use import.meta.env (for example: import.meta.env.VITE_SOMETHING)


In CRA one could check process.env.NODE_ENV value to see if application was build in development or production mode. In Vite this should be changed to check of import.meta.env.DEV or import.meta.env.PROD boolean properties.

No need for %PUBLIC_URL%

While copying some things into new index.html file form CRA version I forgot to remove %PUBLIC_URL% placeholders, these should not be present in Vite version.

Injecting values into views

In CRA I've used preval.macro to inject build timestamp into a diagnostic feature. Maybe it was possible to make it work in Vite too but I went with source transform in vite.config.ts instead:

plugins: [
    name: 'build-timestamp-placeholder',
    transform(src, id) {
      if (id.endsWith('Footer.tsx') && src.includes('BUILD-TIMESTAMP-PLACEHOLDER')) {
        const date = new Date();
        return src.replace('BUILD-TIMESTAMP-PLACEHOLDER', date.toISOString() + date.getTimezoneOffset());

Update (2024-01-28): You can also define global constant replacement to have a built timestamp. This Stack Overflow answer describes it nicely, it looks like a better solution. I'm leaving the part above because it won't hurt to know how to write a source transform :)

Missing robots

When I run Lighthouse on Vite version, it told me that the app was missing robots.txt file (bad from search engines perspective). Indeed, the file was missing, so I copied it to the public folder from CRA version and problem went away.

Missing caching on static files

In CRA version, the static files of built application (*.js, *.css, *.wasm, *.woff2...) were kept in folder named static. In Vite this went to a folder named assets and made Lighthouse rightfully angry about missed opportunity for caching static resources. Since I run my app on NGINX, I had to update a rule that sets caching headers on files from folder named static to the assets folder.

This is how traffic looked like before enabling caching on static files:

Trafic without caching... Click to enlarge...

and this is with caching:

Trafic with caching... Click to enlarge...

Build output directory

When you run a build on CRA the results go into a directory named build, in Vite it goes to dist. I've had a few scripts that assumed build so these had to switch to dist.

Precise file extensions

Vite doesn't like it when a file has *.js or *.ts extension but contains JSX. It turned out that I had one rogue file like it, renamed, fixed.

Tweaking lint rules

The default ESLint rules in Vite were a bit too harsh for my toy project, so I got to add a few exceptions into .eslintrc.cjs config (like '@typescript-eslint/no-non-null-assertion': 'off')

Switching to Vitest

I've heard some good things about Vitest and since full integration of Jest into Vite is currently a bit complicated I decided to give Vitest a try.

This is the test config I have in vite.config.ts:

test: {
  globals: true,
  environment: 'jsdom',
  setupFiles: './src/test/setup.ts',
  // you might want to disable it, if you don't have tests that rely on CSS
  // since parsing CSS is slow
  css: true

and this is the entire content of import src/test/setup.ts;

import '@testing-library/jest-dom';

Aside of config, I had to change usage of jest.fn() to vi.fn() to make the test that use function mocks work.

Oh, one more thing: in CRA/Jest test run complained about one of the files generated for WebAssembly module (maybe it could've been fixed with transformIgnorePatterns in Jest config) but in Vite/Vitest I don't see this problem anymore. 



Once I was happy with how the app was working on a branch created for migration it was time to put Vite on the main (master) branch. This was very easy with the use of merge --strategy=ours (details) because I refrained from making any changes on master while working on the migration. After the merge, I have a clean Vite setup while Git history of files that existed before migration is preserved. Nice.


On localhost

Here's some comparison between the CRA and Vite versions while working on localhost (both after migration to React 18.2.0):

  • Running production build (average of 3 runs, duration as reported by real line in Linux time command output): CRA: 9s, Vite: 4.5s.
  • Starting production build locally with serve -s build in CRA and npm run preview in Vite (average of 3 runs, with time counted from running the command to a functional app appearing in new Chrome tab): CRA 3s, Vite: 0.8s
  • Observing change in a screen while running in DEV mode (hot module reload): CRA: 0.5s, Vite: practically instant :)
  • Running tests: well, frankly speaking I have (currently, yeah) very little tests on that hobby project so I can't offer very meaningful numbers, I can only tell that Vite/Vitest looks about 2.5x faster than CRA/Jest.

To sum up: Vite is noticeably faster but that doesn't mean that CRA version is slow (the difference will start to be significant on a larger application).

On server

What about the deployed application? Unfortunately I don't have data from CRA before updating React so here are the Lighthouse (navigation/desktop with forced clear storage) scores from CRA on React 16.9.0 (left) and Vite on 18.0.2 (right):

Lighthouse scores for CRA vs Vite (navigation, desktop, with forced cache clear)... Click to enlarge...

These are the results for Vite on mobile (sorry, no data for CRA version):

Lighthouse scores for Vite (navigation, mobile, with forced cache clear)... Click to enlarge...

This is the result for mobile but without forced clear storage (so this simulates returning visitor and benefits from static assets cache):

Lighthouse scores for Vite (navigation, mobile, without forced cache clear)... Click to enlarge...


Setting version of assemblies in ASP.NET MVC application with TeamCity build feature


Last five posts (1, 2, 3, 4, 5) were all about fun stuff with Arduino. Now it’s time for something more mundane ;) In this post I will show you how to create TeamCity build that automatically sets version information in all assemblies produced by ASP.NET application. It's nothing new but I hope to give you some useful background info and note a few gotchas you may face...

Complete code of sample application is available in this GitHub repository.

TeamCity has a build feature called AssemblyInfo patcher that makes setting assembly version easy... This feature is usable on any type of .NET project because it works by updating AssemblyInfo files. Content of such files is used to create version information that .NET Framework uses for picking up correct version of referenced assemblies. Version data is also shown in Windows file properties... Here's a part of AssemblyInfo.cs file which is automatically added by Visual Studio when you create a new project:

// Version information for an assembly consists of the following four values:
//      Major Version
//      Minor Version
//      Build Number
//      Revision
// You can specify all the values or you can default the Revision and Build Numbers
// by using the '*' as shown below:
[assembly: AssemblyVersion("")]
[assembly: AssemblyFileVersion("")]

It contains two attributes: AssemblyVersion and AssemblyFileVersion along with a comment that describes numbering pattern recommended by Microsoft. We will also use another attribute: AssemblyInformationalVersion which is not added by default. AssemblyVersion sets version number that is recognized by .NET for dependency resolution. AssemblyFileVersion is used for file version as seen by Windows and AssemblyInformationalVersion is meant more for human consumption as it can contain strings (we will make use of it for holding Git commit hash)... Detailed description of the meaning of these attributes is outside scope of this post but check this great SO answer if you want to know more.



My test application was created in Visual Studio Community 2013 by using ASP.NET Web Application / MVC project template (C#/.NET 4.5). Two additional projects of Class Library type were added. Here’s how the full solution looks:

Visual Studio solution... Click to enlarge...

Home/Index.cshtml view generated by VS was modified to present version information pulled from three .NET assemblies that are produced by the solution (one is for main web app project and two other are for class libraries). Such div was added to the view:

<div class="row text-primary">
    <div class="col-md-12">
            <dt>Core assembly info:</dt>
            <dt>DataAccess assembly:</dt>
            <dt>Web assembly info:</dt>

You can see some Bootstrap classes there since nowadays Visual Studio templates use Bootstrap framework for styling...

This is how rendered view looks before TeamCity processes AssemblyInfo.cs files:

Version information in web app before TC build... Click to enlarge...

And here's how version info looks after version attributes are modified by build feature:

Version information in web app after TC build... Click to enlarge...

If you wonder how the view gets version info here's HomeController.Index action method: 

public ActionResult Index()
    ViewBag.CoreAssemblyInfo = SomeCoreClass.GetAssemblyInfo();
    ViewBag.DataAccessAssemblyInfo = SomeDataAccessClass.GetAssemblyInfo();

    Assembly assembly = Assembly.GetExecutingAssembly();
    string webAsseblyInfo = string.Format("Full Name = \"{0}\"; Informational Version = \"{1}\"",
                            assembly.FullName, FileVersionInfo.GetVersionInfo(assembly.Location).ProductVersion);
    ViewBag.WebAssemblyInfo = webAsseblyInfo;

    return View();

You can see how the most important assembly version number (the one used by .NET and designated by AssemblyVersion attribute) is a part of assembly's FullName. Informational version (the one that can have strings) is taken with the help of FileVersionInfo class. You can get the number form AssemblyFileVersion attribute too - just check all the interesting stuff that GetVersionInfo method returns... The same kind of code is used in GetAssemblyInfo methods in SomeCoreClass and SomeDataAccessClass.

Ok, so we have our test application - full code is here. Note: I’ve pushed all used Nuget packages to the repository – that takes some space in the repo and might be against recommended way of using Git but it makes TeamCity setup easier. If packages folder is not committed you can expect this type of error during build:

[Csc] App_Start\BundleConfig.cs(2, 18): error CS0234: The type or namespace name 'Optimization' does not exist in the namespace 'System.Web' (are you missing an assembly reference?)

To solve it you would have to restore Nuget packages during build (here’s some info on how to do it).



Now time for build server config! I assume that you have some working knowledge about setting TeamCity build for .NET application so I will discuss only the steps relevant to versioning. I’ve used TeamCity 9.1.3 but don't worry if you have a bit older TC (AssemblyInfo patcher feature exists for a while). I used TC to build code from Git repository checkout on my local drive...

Before setting up AssemblyInfo patcher, add two new build parameters: Minor and Major. These are meant to represent two initial segments of version number and should be set manually - it's your (technical/marketing?) decision whether to name your next version 1.9 or 2.0, right? 

Major and Minor build parameters... Click to enlarge...

Next step is to add AssemblyInfo patcher build feature:

AssemblyInfo patcher build feature... Click to enlarge settings...

And set its properties:

AssemblyInfo patcher settings... Click to enlarge...

I've decided to use such settings:

  • AssemblyVersion:   %Major%.%Minor%.%build.number%
  • AssemblyFileVersion:   %Major%.%Minor%.%build.number%
  • AssemblyInformationalVersion:   %Major%.%Minor%.%build.number%.%build.vcs.number%

You can see that our Major and Minor parameters are used. You can also see the use of TeamCity built-in parameter named build.number. Last attribute contains another TeamCity param: build.vcs.number. It gets version control revision id. I'm using Git so this is a long alphanumerical SHA-1 hash. It means that it cannot be used in setting AssemblyVersion attribute. If you try to do so you will get an error like this:

[Csc] Properties\AssemblyInfo.cs(35, 12): error CS0647: Error emitting 'System.Reflection.AssemblyVersionAttribute' attribute -- 'The version specified '' is invalid'

If you try to use it for AssemblyFileVersion you can expect a warning: 

[Csc] CSC warning CS1607: Assembly generation -- The version '' specified for the 'file version' is not in the normal 'major.minor.build.revision' format

But you can safely use it in AssemblyInformationalVersion as .NET doesn't care if you put letters there... Note: If you work with SVN instead of Git you are lucky because value returned for build.vcs.number is an integer and can be used in all three version-related attributes. If you really need to set revision in AssemblyVersion while using Git you might need to add a custom build step for creating integer id... Let's keep it simple here and leave the last part of version number intact (as 0)...

Once you have AssemblyInfo patcher feature configured and you run the build, you can expect such entries in the build log: 

[22:46:02]Step 1/1: Visual Studio (sln) (2s)
[22:46:02][Step 1/1] Update assembly versions: Scanning checkout directory for assembly information related files to update version to 2.1.14
[22:46:02][Update assembly versions] Updating assembly version in C:\TeamCity\buildAgent\work\8c2a410f7087e36b\.NET\AssemblyInfoTest\AssemblyInfoTest\Properties\AssemblyInfo.cs
[22:46:02][Update assembly versions] Updating assembly version in C:\TeamCity\buildAgent\work\8c2a410f7087e36b\.NET\AssemblyInfoTest\Core\Properties\AssemblyInfo.cs
[22:46:02][Update assembly versions] Updating assembly version in C:\TeamCity\buildAgent\work\8c2a410f7087e36b\.NET\AssemblyInfoTest\DataAccess\Properties\AssemblyInfo.cs

If all went ok your log should also contain something like this:

[22:46:05]Reverting patched assembly versions
[22:46:05][Reverting patched assembly versions] Restoring C:\TeamCity\buildAgent\work\8c2a410f7087e36b\.NET\AssemblyInfoTest\AssemblyInfoTest\Properties\AssemblyInfo.cs
[22:46:05][Reverting patched assembly versions] Restoring C:\TeamCity\buildAgent\work\8c2a410f7087e36b\.NET\AssemblyInfoTest\Core\Properties\AssemblyInfo.cs
[22:46:05][Reverting patched assembly versions] Restoring C:\TeamCity\buildAgent\work\8c2a410f7087e36b\.NET\AssemblyInfoTest\DataAccess\Properties\AssemblyInfo.cs

Don't worry, reverting takes place only in build agent work files. The build artifacts contain properly versioned assemblies. You've seen a proof of that rendered on HTML page, you can also check DLL files properties:

File properties with version information... Click to enlarge...

Properties window shows version set by AssemblyFileVersion and AssemblyInformationalVersion. I have Polish Windows so the properties are labeled Wersja pliku (it means File version) and Wersja produktu (it means Product version).

Keep in mind that AssemblyInfo patcher will not work if version attribute has non-standard format (or AssemblyInfo files are in unusual locations).

Let's say you have something like this (because you keep information about your product in static class constants):

[assembly: AssemblyVersion(ProductInfo.Version)]

You can expect such warning during build:

[Update assembly versions] Assembly info version was specified, but couldn't be patched in file C:\TeamCity\buildAgent\work\8c2a410f7087e36b\.NET\AssemblyInfoTest\AssemblyInfoTest\Properties\AssemblyInfo.cs. Is necessary attribute missing?



And that's all! We have a TeamCity build that sets version information in ASP.NET MVC application assemblies :) 

If somebody will be interested I can write a little supplement to this post in which I will describe how to add version info into zip package (artifact) and how to display it on Team City UI...