🎉 Guide complete

You now know exactly what you're missing.

What you covered

💡 The Bottom Line, one more time

Going from TypeScript back to plain JavaScript is a loss, not a lateral move — there's no syntax to swap in, because the thing you're losing (a compile-time type checker) simply has no JavaScript equivalent. You lose write-time error catching, editor autocomplete driven by declared shapes, guaranteed object shapes from interface, and the consistency guarantee generics gave containers. Nothing fully replaces any of that. What partially compensates: JSDoc comments plus @ts-check/checkJs claw back real editor checking without a build step; manual typeof/instanceof guard clauses and thrown errors at boundaries convert silent failures into loud, immediate ones; and knowing the specific everyday traps — coercion, null vs undefined, unchecked switch cases — means you're at least watching for them deliberately instead of trusting a compiler that's no longer there.

What's next

This guide covered what changes and how to cope. From here, the natural next steps are:

Go back to TypeScript, if you have any choice in the matter — everything in this guide was about coping with the loss, not arguing that the loss is a good trade. If the project can adopt (or re-adopt) TypeScript, that remains the strongest option by a wide margin.
Adopt JSDoc + checkJs as a middle ground — if a full TypeScript migration isn't practical right now, turning on project-wide checkJs and writing JSDoc annotations incrementally (starting with your most-used or most bug-prone files) recovers a real amount of the safety net with a fraction of the migration effort.
The full JavaScript Fundamentals track — worth revisiting even as an experienced developer, since plain JavaScript's dynamic-typing quirks (coercion, this binding, prototypal inheritance) are exactly what TypeScript's checks were quietly smoothing over, and this guide only covered the parts of that gap specific to losing types.

More transition guides (Oracle → SQL Server, SQL Server → MySQL) are on the way — no need to go looking elsewhere.

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