Check out any tutorial on how to configure TypeScript + Webpack. Create one empty script file in Construct 3, save the project as a folder, and make Webpack build a bundle along the path of this script, and that's it. Yes, you will have to click "Update scripts from folder" every time you change your scripts, but this is not such a problem. I've been doing this for months. Now the project is 5K lines in TypeScript. I feel pretty good.
The webpack also allows you to use NPM packages without any problems.
Super old topic, but did you write TS definition files for Construct's builtin types?
Somewhat related, has anyone written extensions for VS Code, Sublime, or any other external IDE that supports autocomplete for Construct?