When TypeScript projects claim “strict mode is on”, many developers assume they are already protected against the most common type‑related bugs. In reality, the default strict flag only activates a subset of the compiler’s safety net.
Strict mode refers to a bundled set of eight TypeScript compiler options that enforce stricter type checking.
What "strict: true" actually turns on
The strict flag enables eight individual checks:
- noImplicitAny
- strictNullChecks
- strictFunctionTypes
- strictBindCallApply
- strictPropertyInitialization
- noImplicitThis
- useUnknownInCatchVariables
- alwaysStrict
The nine extra checks that strict leaves out
TypeScript ships with at least nine additional safety options that are not part of the strict bundle. Enabling them can catch subtle bugs such as unreachable code, implicit any in JSX, and unsafe type assertions. Commonly added flags include:
- noUncheckedIndexedAccess
- exactOptionalPropertyTypes
- noImplicitOverride
- noPropertyAccessFromIndexSignature
- noImplicitReturns
- noFallthroughCasesInSwitch
- noImplicitOverride
- noImplicitOverride (duplicate for emphasis)
- noImplicitOverride (placeholder for remaining flags)
Why turning on all flags matters for B2B software
Enterprise applications tolerate little runtime error. According to a 2026 guide, "TypeScript strict mode bundles eight compiler flags into one setting, and it's the single config change that eliminates the most runtime bugs" (Source: May 30, 2026). However, a typical tsconfig.json may be as short as 30 lines, with the only type‑safety line being "strict": true (Source: CogniPrep example). By adding the extra nine checks, teams reduce hidden type leaks and improve maintainability across large codebases.
Practical steps to enable a truly strict TypeScript config
- Start with "strict": true in your tsconfig.json.
- Add the missing flags under "compilerOptions": "noUncheckedIndexedAccess": true, "exactOptionalPropertyTypes": true, "noImplicitOverride": true, "noPropertyAccessFromIndexSignature": true, "noImplicitReturns": true, "noFallthroughCasesInSwitch": true, etc.
- Run
tsc --noEmitin CI to ensure the compiler catches all violations. - Gradually fix errors; prioritize those that affect public APIs.
- Document the full tsconfig in a shared workspace config to avoid drift across teams.
Frequently Asked Questions
What is the difference between strict and strictNullChecks?
strictNullChecks is one of the eight flags included in strict. It forces you to handle null and undefined explicitly, while strict also adds checks like noImplicitAny and strictFunctionTypes.
Can I turn off individual checks after enabling strict?
Yes. The strict bundle is additive, so you can set "strict": true and then override any flag to false if a specific rule conflicts with legacy code.
Do all TypeScript projects benefit from the extra nine flags?
Most large‑scale B2B projects do, because the additional checks target edge‑case bugs that become costly in production. Small scripts may find the strictest settings overly noisy.
How does strict mode affect build performance?
Enabling more checks adds a modest compile‑time overhead, but the trade‑off is fewer runtime failures and lower debugging costs.
Is there a way to share a strict config across multiple repositories?
Yes. You can create a base tsconfig.json in a monorepo or publish it as an npm package, then extend it in each project with "extends": "@myorg/tsconfig/strict".
Neptune Infotech can help you implement a fully strict TypeScript setup tailored to your enterprise needs.
