How often have you needed to modernize a legacy frontend application and re-build them using a more modern technology/framework like React/Angular etc.?

At my current job, I have to migrate a JQuery dashboard to React. I was wondering what other people's experience has been in this regard.

• What was the most painful part of migrating an existing app to React/Angular?

• What were some of the pitfalls that I should look out for?

• If you had to do it again, what would you do differently?