Instruction: Explain what strictNullChecks does and how it affects type checking and error handling in TypeScript.
Context: This question evaluates the candidate's understanding of TypeScript's compiler options, specifically strictNullChecks, and its significance in enhancing type safety and reducing runtime errors.
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With strictNullChecks enabled, TypeScript treats null and undefined as distinct types. This means variables, parameters, and return types are checked more strictly, and assigning null or undefined to them without explicit declaration will result in a compile-time error. This feature significantly enhances type safety, as it prevents many common mistakes related to nullability that can lead to runtime errors.
For instance, consider a function designed to fetch user data. Without strictNullChecks, if the data source is temporarily unavailable leading to a null or undefined return value, the application might proceed without error during compilation but could crash or behave unexpectedly at runtime when trying to access properties on what it assumes to be a valid user object. By contrast, with strictNullChecks enabled, TypeScript...