tsconfig.json: The Settings That Matter

30‑second interview answer

tsconfig.json controls how TypeScript checks and emits code. The most important choice is enabling strict mode for correctness. In frontend projects, jsx, lib, and moduleResolution affect compatibility, while options like noUncheckedIndexedAccess can catch real bugs. For large repos, incremental builds speed up compilation.

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The high-impact options

strict

Turns on a bundle of checks:

• noImplicitAny
• strictNullChecks
• more

Interview stance:

“Strict mode is worth it for long-term maintainability.”

strictNullChecks

Forces you to handle null/undefined.

noImplicitAny

Prevents silent any.

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Frontend-specific options

• jsx: preserve / react-jsx
• lib: include DOM/ES features
• module + moduleResolution: ESM/CJS behavior

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Incremental builds

• incremental: true
• tsBuildInfoFile

Helps speed in large codebases.

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Common mistakes

• Turning off strict to “fix errors fast”
• Not including dom in lib for browser apps

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Mini Q&A

Q1: Why strict mode?

• fewer runtime bugs.

Q2: What does strictNullChecks do?

• null/undefined must be handled.

Q3: Why incremental?

• faster rebuilds.

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Summary checklist

• I know strict is the big one.
• I can explain strictNullChecks.
• I can explain jsx/moduleResolution basics.
• I know incremental build benefits.