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strict-mode

Strict mode flags

Last reviewed May 28, 2026 Content v20260528
Track mode
client_typescript
Means
In-browser TS
Reading
~1 min
Level
advanced

This lesson

This lesson teaches Strict mode flags—the ideas, syntax, and habits you need before moving on in TypeScript.

Strict compiler settings are the default on professional TS projects; learn them before a codebase fights you.

You will apply Strict mode flags in contexts like: Modern front-end apps, Node APIs, and any team that standardizes on TS-first tooling.

Write TypeScript, compile in the browser, run the emitted JavaScript, and check understanding with MCQs.

When intermediate lessons feel comfortable and you are ready for production-style trade-offs.

strictNullChecks, noImplicitAny, strictFunctionTypes, and friends catch entire bug classes. Enable strict on new projects.

Flag highlights

  • noImplicitAny — untyped parameters become errors
  • strictNullChecks — nullability respected
  • noUncheckedIndexedAccess — index access may be undefined

Self-check

  1. Name one bug strictNullChecks prevents in UI code.

Turn on strict early; retrofiting a large codebase later is far more expensive than fixing violations lesson by lesson.

Tip: Enable strict on greenfield repos—retrofits are painful.

Interview prep

What does strict enable?

A family of flags including strictNullChecks and noImplicitAny for safer defaults.

Interview tip Lesson completion confidence

Can you explain this lesson in 30 seconds without reading notes?

Not saved yet.

Playground

Runs in your browser in a sandboxed frame. Backend runners appear when this track’s profile allows them.

Check yourself

Multiple choice — immediate feedback.

Discussion

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Starter discussion topics

  • What part of this lesson needs a second read?
  • What would you try differently in a real project?

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