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Creating a tramvai library

Adding a new library or module to the tramvai repository is detailed in the Contribute section

This guide contains a set of tips for developing individual tramvai packages in application repositories, also, many teams maintain separate monoreps with common packages for a number of applications, divided into different repositories.


Let's consider all important cases using the example of creating a new tramvai module. Let's say the module will provide a new HTTP client to work with the Github API.

Package name

It is highly discouraged to use the @tramvai and @tramvai-tinkoff scopes outside the tramvai repository. If our application is called tincoin, you can, for example, select one of these scopes:

  • @tincoin
  • @tramvai-tincoin
  • @tincoin-core

For modules, the prefix is ​​usually module-, for example: @tramvai-tincoin/module-github-api-client


The choice of a versioning strategy is entirely yours. We definitely recommend following semver, and we can recommend using unified versioning if:

  • you support monorep with core libraries
  • these libraries can be linked
  • and these packages are used in applications all together (or most of them)


Dealing with library dependencies is not an easy task, and there is no ideal solution, but there are a number of tips to make it easier to manage dependencies. The best place to start is by dividing dependencies into different types:


Examples of such dependencies are react and react-dom, @tramvai/* and @tramvai-tinkoff/*. If we write babel or eslint plugin, it can be @babel/core and eslint.

Typically, an end user, such as a tramvai application, is required to install a dependency framework, without them it simply won't work.

Therefore, our library should set them to peerDependencies, with the most free versions, for example, if the package is tied to the basic functionality of tramvai, and uses React hooks:

"peerDependencies": {
"@tramvai/core": "*",
"react": ">=16.8",
"react-dom": ">=16.8"


A number of dependencies must be strictly one in the application. Any duplicates are a minus. increase the weight of the application bundle, but libraries such as react or @tinkoff/logger require a single copy in our application.

For them, the rule applies as with the framework, you need to install them in peerDependencies, with the most free versions:

"peerDependencies": {
"@tinkoff/logger": "*"

Many packages are popular enough that chances are they are already being used in the final application. An example of such dependencies is - date-fns, lru-cache, @tinkoff/dippy

For them, the rule applies as with the framework, you need to install them in peerDependencies, with the most free versions:

"peerDependencies": {
"@tinkoff/dippy": "*",
"date-fns": ">=2",
"lru-cache": "*"


Let's say our new tramvai module delivers unique functionality to the application that requires a third-party library (or even another package in your monorepo)

If we are developing a service to work with the Github API, it might be the @octokit/rest package.

In this case, you need to put the library in dependencies, and you can leave the standard range using ^:

"dependencies": {
"@octokit/rest": "^18.0.0"


A dependency may be involved in building your package - for example, rollup or @tramvai/build. The dependency is required to run library tests. The dependency contains the taipings required for the build.

In all these cases, even if either is already in peerDependencies, it is worth adding a more specific version to devDependencies, for example:

"devDependencies": {
"@tramvai/build": "^2.5.0",
"@types/react": "^17.0.0",
"react": "^17.0.0"


Of course, there are exceptional cases.

For example, tramvai provides many test utilities where all the main @tramvai dependencies were in peerDependencies. As soon as these utilities began to be used not in repositories with applications, but in monoreps with core packages, the problem of missing dependencies appeared, and we moved almost everything from peerDependencies to dependencies

Proceed according to the situation and always think about the usability of your product :)


It is assumed that the final assembly of packages in the context of the application will be done by @tramvai/cli. Therefore, to publish packages written in TypeScript, it suffices to use tsc, and publish many compiled .js and .d.ts files.

But building packages into bundles before publishing, for example via rollup or @tramvai/build, gives a number of possibilities:

  • preliminary tree-shaking will cut off all unnecessary, this will have a positive effect on the assembly of the application
  • you can make several bundles for different environments, in CJS or ES modules formats
  • you can make a separate bundle for the browser build, separate for the server one - top for libraries with SSR support

Detailed documentation on using @tramvai/build is available in documentation


Some of useful articles about tree-shaking:

Summarizing all the optimizations needed to create tree-shakable libraries:

  • Prevent TypeScript decorators usage

    Explanation: Terser can't remove unused exports in transpiled code with decorators, both Babel or tsc add utility functions, potentially with side-effects for Terser

  • Prevent static properties usage for React functional components

    Explanation: Terser can't remove unused components in transpiled code when more than one static properties are used

  • Use ES modules for server and browser build, CJS only for backward compatibility

  • Split the library logic into small modules

  • Preserve file structure of this modules during the bundling

    Explanation: Webpack can remove unused code from modules graph, and we don't have to worry about removing this code with Terser

  • Add "sideEffects": false field to package.json (or specify an array of files that cannot be cut - "sideEffects": ["some-global.css"])

  • Always test tree-shaking of your packages on the default webpack production build, add the magic comment /* @__PURE__ */ if necessary

    Explanation: /* @__PURE__ */ helps Terser to understand that the called function has no side effects

Modern ES code

Reference articles:

Transpiling the source code into ES2019 for the browser build will help deliver significantly less code to the client. For backward compatibility with older browsers, you need to transpile node_modules with modern code via Babel, when building your application to production. @tramvai/cli will do this transpilation automatically for tramvai applications.


The @tramvai/build tool out of the box gives you some of this optimizations:

  • CJS and ES modules builds
  • Modern JS code
  • File structure preservation
  • Support for separate browser build

So, this tool is recommended by tramvai team for building any packages used by any SSR applications.

Get started with @tramvai/build