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I just learned JavaScript, and rewriting my whole project in TypeScript from scratch sounds like starting over.
What you'll have at the end
One JavaScript file in the project, now a real TypeScript file, passing a full type check with zero errors, while every other file in the project is untouched and still runs exactly as before.
You need
A JavaScript project you can already run, with a package manager already set up, and one specific file in it that you've picked to convert first.
Not covered
Turning on the project's strictest checks, or converting a second file: this gets one file to a clean, honest baseline and stops there.
Leans on
Why can't TypeScript find types for a package you just installed?
For when the checker's own complaint is about a package's missing types rather than your own code, once this file starts importing something from outside the project.
Fix an object is possibly undefined error
For a completely different error shape: a value the checker is sure could be missing, rather than a shape it was never told about.
Checked 22 Aug 2026
Part of the TypeScript cookbook