Frontend
Language contracts, runtime behavior, and types that pay rent at system boundaries.
TypeScript · JavaScript · 4 published · 22 in the review queue. Written by Al Beltran.
Interview Lab
TypeScript Interview Questions, With the Reasoning
Types at boundaries, narrowing, generics, and the questions that separate autocomplete from design.
Frontend
TypeScript as an API Contract, Not a Costume
Share types across producer and consumer, validate at the edge, and stop trusting JSON because it compiled once.
Interview Lab
JavaScript Interview Questions, With the Reasoning
Closures, the event loop, equality, and this — explained as runtime behavior, not trivia.
The interesting TypeScript story is not frontend fashion. It is the language teams use to glue APIs, workers, and infrastructure code that used to be a pile of untyped scripts.
Planned notes stay unpublished until they are written and reviewed. Titles are listed so the topic map is complete. They are not pages.
unknown vs any: One Forces a Decision
Why any disables the checker and unknown just postpones the cast until you know the shape.
comparison · beginner · medium priority
Discriminated Unions for States That Cannot Be Two Things
Model idle / loading / error / success as a union so impossible props do not compile.
educational · intermediate · medium priority
Generics Without Turning the File Into a Puzzle
One type parameter that captures a relationship. Not four that impress no one in review.
educational · intermediate · medium priority
The Event Loop for People Who Also Write Servers
Microtasks, macrotasks, and why a tight CPU loop starves HTTP in Node the same way it starves paint in the browser.
educational · intermediate · medium priority
Closures in Production: Leaks, Stale Values, and Useful Privacy
When a closure is the right module boundary, and when it holds a whole response in memory.
educational · intermediate · medium priority
Equality and Coercion: Write === and Still Know ==
What interviewers want when they ask about ==, and why production code should not rely on it.
educational · beginner · medium priority
Narrow Types at the Boundary, Trust Them Inside
Parse once. Do not sprinkle as Foo through a service that already decided the shape.
architecture · intermediate · medium priority
Utility Types That Earn Rent: Pick, Omit, and Record
The three utilities that show up in real APIs, and the ones that usually mean you wanted a new type.
educational · intermediate · medium priority
Promises vs async/await: Same Machine, Different Readability
When to Promise.all, when sequential await is the bug, and how errors surface in each style.
comparison · intermediate · medium priority
this Binding Without the Mythology
Call site, bind, arrows, and the class methods that lose this in a callback.
educational · intermediate · medium priority
Runtime Validation at the Edge (Zod or Equivalent)
TypeScript disappears at runtime. A schema at the HTTP or queue boundary is the real contract.
architecture · intermediate · medium priority
ESM vs CommonJS: The Interop Bugs You Will Hit
default export traps, dual packages, and why "it works in the test file" is not a module strategy.
troubleshooting · intermediate · medium priority
Migrating a JavaScript Service to strict TypeScript
File by file, boundary first. Do not flip strict on a 40k-line folder and call it a week.
problem-solving · senior · medium priority
Iterators and Generators When Streaming Is the Point
When a generator is a real API, and when it is a party trick in a CRUD handler.
educational · intermediate · medium priority
When to Write a Declaration File (and When to Fork the Types)
Ambient modules, untyped deps, and the cost of a local .d.ts that lies.
educational · intermediate · medium priority
JavaScript Memory Leaks in Long-Lived SPAs
Listeners, closures over large trees, and detached DOM that never quite dies.
troubleshooting · intermediate · medium priority
Branded Types for IDs So You Stop Passing the Wrong UUID
A light brand on UserId vs OrderId. Not a new type system religion.
architecture · intermediate · medium priority
Error Handling Patterns That Leave a Trace
Operational vs programmer errors, cause chains, and what to return on an API.
educational · intermediate · medium priority
infer and Conditional Types: Read Them Before You Write Them
Useful for libraries. Usually the wrong move in an application service.
educational · senior · medium priority
Debounce, Throttle, and requestAnimationFrame
Which one belongs on search, which on scroll, and which on a canvas frame.
problem-solving · intermediate · medium priority
TypeScript Enums vs String Unions
Why most application code should prefer a union, and when a const object is enough.
comparison · intermediate · medium priority
Prototypes and Classes: The Same Object Model
What class syntax desugars to, and why you still need to know the prototype chain.
educational · intermediate · medium priority