TypeScript Interview Questions - Coding Interview 2026

Show how interfaces in TypeScript type objects like user, with required id and name, enable safe, reusable code and autocomplete in functions such as getName.

Define reusable types in TypeScript with the reserved type keyword, creating an id type and a users array to show readability and maintainability across string and number data.

Explore how to narrow unions in TypeScript by using a specific property for type narrowing and instance of checks to access success, failed, or loading state and related data.

Explore the difference between void and never in TypeScript, showing when a function ends with a throw, and why never indicates no reachable end while void means no return value.

Explore how TypeScript works with the DOM, using typecasting and type assertions to safely access elements and values. Learn about nullability, element narrowing, and typed events.

Explore how TypeScript adds typed properties, constructors, and access modifiers to classes, and shows interfaces, implements, static members, and class extension with user and admin examples.

TypeScript enums store related constants as a type and value, offering numeric defaults and string values for statuses like not started, in progress, and done.

Explain the difference between arrays and tuples in TypeScript, with square-bracket arrays, unions, and fixed-length tuples, and show why enums or interfaces improve readability.

Learn to type dynamic keys in a user object by replacing a string-typed columns array with key of user, preventing any and ensuring only id, name, and age are valid.

Learn to derive new types by omitting or picking properties from existing interfaces or types using TypeScript's omit and pick utilities to enable reuse without copy-pasting.

Explore how to use the read only helper in TypeScript to wrap a user type, making all properties read only and preventing writes like user.name.

Explore how the Partial helper in TypeScript marks all interface properties optional, allowing safe partial updates by merging a user with only the fields to update.

Explore tsconfig.json, the TypeScript project configuration file in the root folder, detailing include, compilerOptions such as target, module, moduleResolution, lib, and strict linting to catch errors.

Learn to transpile TypeScript to JavaScript with the TypeScript Command Line Tool (TSC), specify source and output files, and see how types are removed in the final JavaScript.

Explore the advanced section of TypeScript, focusing on library design and low-level typings, and understand why typing inside TypeScript suits libraries but not everyday projects.

Implement a generic utility type if that selects between T and F based on a boolean C; if C extends true it returns T, else F.