Advanced TypeScript Workshop: Structural and Conditional Typing, Discriminated Unions, Mapped Types

Senior Software Engineer Adam Rackes (Spotify) joins the JS Drop to go deep on advanced TypeScript concepts that most devs only scratch the surface of. In a packed live coding session, Adam demystifies structural typing, unions and narrowing, conditional types, discriminated unions, variance, and mapped types, walking through real-world gotchas and tricks for using TypeScript to its full potential. Keypoints from this episode: Structural vs. Nominal Typing: Adam explains how TypeScript’s structural typing model differs from nominal typing in languages like Java and C#, and why it matters for real-world dev workflows. Narrowing Techniques: He walks through four ways to narrow union types—including in, typeof, instanceof, and discriminated unions—with practical examples and when to use each. Conditional & Mapped Types: The episode digs into how extends, infer, and template literal types work under the hood, including how to extract types from functions and reshape object types dynamically. Variance in Function Types: Adam breaks down why function parameters are contravariant in TypeScript and how that affects type safety when assigning functions with different type signatures. Follow Adam Rackis on Social Media Twitter: https://x.com/AdamRackis Linkedin:   / adam-rackis-5b655a8   Sponsored by This Dot: thisdotlabs.com