Migrating a Legacy JavaScript Codebase to TypeScript - JSJ 680
JavaScript Jabber5 Kesä 2025

Migrating a Legacy JavaScript Codebase to TypeScript - JSJ 680

In this episode, Dan and I (Steve) dove deep into what turned out to be a surprisingly complex, yet incredibly insightful topic: gradually migrating a massive legacy JavaScript project over to TypeScript. We're talking about nearly 1,000 JS files, 70,000+ lines of code, and years of developer history—all transitioning carefully to a typed, modern future.

Dan walked us through how he started by setting up the project for success before converting even one file—getting CI/CD ready, setting up tsconfig.json, sorting out test dependencies, dealing with mock leaks, and even grappling with quirks between VS Code and WebStorm debugging.

We talked tools (like TS-ESLint, concurrently, and ts-node), why strict typing actually uncovered real bugs (and made the code better!), and why it’s crucial not to touch any .js files until your TypeScript setup is rock solid.

Key Takeaways:
  • Gradual migration is 100% possible—and often better—than ripping the bandaid off.
  • TypeScript can and will catch bugs hiding in your JavaScript. Be prepared!
  • Use VS Code extensions or TS-Node to support your devs’ tooling preferences.
  • Don't underestimate the setup phase—it’s the foundation of long-term success.
  • Start small: Dan's team converted just one file at first to test the whole pipeline.
If you’re sitting on a legacy JS project and dreaming of TypeScript, this episode is your blueprint—and your warning sign.

Become a supporter of this podcast: https://www.spreaker.com/podcast/javascript-jabber--6102064/support.

Jaksot(737)

009 JSJ Testing JavaScript with Joe Eames

009 JSJ Testing JavaScript with Joe Eames

The panelists discuss testing JavaScript with Joe EamesSpecial Guest: Joe Eames. Support this podcast at — https://redcircle.com/javascript-jabber/donationsPrivacy & Opt-Out: https://redcircle.com/p...

27 Maalis 20121min

008 JSJ V8 and Dart with Lars Bak and Kasper Lund

008 JSJ V8 and Dart with Lars Bak and Kasper Lund

The panelists discuss V8 and Dart with Lars Bak and Kasper Lund.Special Guest: Kasper Lund. Support this podcast at — https://redcircle.com/javascript-jabber/donationsPrivacy & Opt-Out: https://redc...

14 Maalis 201247min

007 JSJ Online Resources for Javascript Developers

007 JSJ Online Resources for Javascript Developers

The panelists discuss online resources for JavaScript Developers. Support this podcast at — https://redcircle.com/javascript-jabber/donationsPrivacy & Opt-Out: https://redcircle.com/privacyBecome a ...

13 Maalis 201230min

006 JSJ Chrome Dev Tools with Paul Irish

006 JSJ Chrome Dev Tools with Paul Irish

The panelists discuss Chrome dev tools with Paul Irish.Special Guest: Paul Irish. Support this podcast at — https://redcircle.com/javascript-jabber/donationsPrivacy & Opt-Out: https://redcircle.com/...

24 Helmi 201251min

005 JSJ Javascript Objects

005 JSJ Javascript Objects

The panelists discuss JavaScript objects. Support this podcast at — https://redcircle.com/javascript-jabber/donationsPrivacy & Opt-Out: https://redcircle.com/privacyBecome a supporter of this podcas...

18 Helmi 201253min

004 JSJ Backbone.js with Jeremy Ashkenas

004 JSJ Backbone.js with Jeremy Ashkenas

The panelists discuss Backbone.js with Jeremy Ashkenas.Special Guest: Jeremy Ashkenas . Support this podcast at — https://redcircle.com/javascript-jabber/donationsPrivacy & Opt-Out: https://redcircl...

13 Helmi 201254min

003 JSJ Build Tools

003 JSJ Build Tools

The panelists discuss build tools. Support this podcast at — https://redcircle.com/javascript-jabber/donationsPrivacy & Opt-Out: https://redcircle.com/privacyBecome a supporter of this podcast: http...

3 Helmi 201245min

002 JSJ The Right Way to Build Web Applications

002 JSJ The Right Way to Build Web Applications

The panelists discuss the right way to build web applications. Support this podcast at — https://redcircle.com/javascript-jabber/donationsPrivacy & Opt-Out: https://redcircle.com/privacyBecome a sup...

29 Tammi 201248min

Suosittua kategoriassa Liike-elämä ja talous

sijotuskasti
psykopodiaa-podcast
mimmit-sijoittaa
rss-rahapodi
rss-lahtijat
rss-draivi
rss-porssipuhetta
rahapuhetta
oppimisen-psykologia
rss-rahamania
rss-seuraava-potilas
rss-neuvottelija-sami-miettinen
rss-bisnesta-bebeja
rss-paatos-podcast-suomen-kovimmat-paatoksentekijat-2
rss-paasipodi
rss-40-ajatusta-aanesta
taloudellinen-mielenrauha
syo-nuku-saasta
kasvun-kipuja
rss-viisas-raha-podi