Developing in a Large Monorepo
In Microsoft, we have a very large TypeScript-based git repository where over 250 developers build and write code for high-value frontend components which is used across all Microsoft365 products like Outlook, Office, Bing, SharePoint, etc.It contains over a 100 npm packages, containing over a million lines of TypeScript code. Co-locating these components encourages collaboration and sharing code across teams very easier.
In this talk, we’ll focus on the tooling used and code organization to make the development easier, fast and reliable and will not discuss in detail unit tests and automation for a better focus on development.
A closer look at package management
Since there are 100+ highly inter-connected internal npm packages which declare over 2,500 external dependencies, we will briefly take a look at how packages and dependency management. We will discuss the structure of each package in the monorepo and how dependencies are expressed across these packages.
The packages contain transpiled TypeScript code and bundles generated using webpack and the modules from these bundles are used across various product endpoints.
Handling package dependencies
We use yarn workspaces to install our external dependencies and link the Midgard-hosted packages together based on the dependencies expressed in the package.json files. We will use an example with yarn workspaces to handle package dependencies in a sample monorepo.
The other major part of managing monorepos is cross-package orchestration. We would want to execute scripts across all the packages easily like build/packaging commands, linting, etc. We will take a look at achieve this using Lerna through the talk.
Using Test Apps to validate user behaviour
To validate more complex component behaviors, like user interactions, we use test-apps. Test apps are either webpages or native applications which load our bundles to render our components for manual testing. This is probably the second most popular validation workflow, therefore we care a lot about it.
Improving “watch” across packages
We will also briefly look at how we will manage watch processes for the monorepo-hosted packages. Its also important to discuss the Intellisense performance here.
We will go over a sample monorepo structure to explain this in detail.