See my blog post for details: How to set up a typescript project for Power Apps Web Resources

Build

npm install
npx webpack

This will build typescript code and bundle the javascript into js files and place them in the dist folder

Usage

• Deploy the js files from dist folder as web resources in Power Apps
• Define the function name with pattern [LibraryName].[FunctionName] (e.g. Account.accountOnLoad) in Power Apps handler