This directory contains the new TypeScript based code. TS code is compiled into JS and used in the v2 of the website.
The build uses npm. Install it and run (from this directory):
# Install the dependencies.
npm install
# Build the code.
# This will write build artifacts to out/ directory and write a
# combined JS file at //src/website/static/ts/bundle.js.
npm run build
# Run tests.
npm run test