Strict Mode and noImplicitAny

Strict checking is one of the highest-value choices in a new codebase. strictNullChecks makes null and undefined distinct concerns; noImplicitAny flags values whose types would otherwise silently become any; strictFunctionTypes tightens function parameter compatibility in relevant positions.

Enable strictness early, then fix errors at their source. Do not silence every error with any or as SomeType: doing so removes the evidence the compiler is providing. For legacy migrations, enable checks incrementally and track unsafe areas explicitly.

Handle an optional value

function getDisplayName(name: string | undefined): string {
  if (name === undefined) {
    return "Guest";
  }
  return name.toUpperCase();
}

💡 The guard narrows name from string | undefined to string in the remaining branch, making the call safe under strict null checking.

Key Takeaways

Prefer strict mode for new projects.
Narrow nullable values rather than hiding the error.
Use unknown at uncertain boundaries instead of defaulting to any.

Knowledge Check

With `strictNullChecks` enabled, what is true of `string | undefined`?

Strict Mode and noImplicitAny

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