JavaScript Set Methods Accept Set-Like Objects, Not Arbitrary Iterables
Use union, intersection, difference, and Set predicates with the size, has, and keys set-like protocol.
JavaScript technical articles
JavaScript articles for working developers
Clear explanations of the details that shape real programs.
Explore JavaScript runtime behavior, language semantics, browser APIs, and the edge cases that affect production code.
Latest articles
15 articles
Object.groupBy and Map.groupBy Use Different Kinds of Keys
Choose Object.groupBy or Map.groupBy based on property-key coercion, object identity, symbols, and result access.
JavaScript RegExp lastIndex Makes Global and Sticky Matching Stateful
Control RegExp lastIndex safely with global and sticky matches, zero-length patterns, test, exec, and matchAll.
JavaScript Equality Algorithms: ===, Object.is, and SameValueZero
Choose the right JavaScript equality rule for NaN, signed zero, array searches, and Map or Set keys.
JavaScript Private Fields Use Brand Checks, Not Property Names
How #private fields enforce class identity across inheritance, proxies, static members, and explicit brand checks.
Promise.all, allSettled, any, and race Fail Differently
Choose a Promise combinator by its failure result, ordering guarantees, and whether you need explicit cancellation for unfinished work.
The Event Loop Is Really a Collection of Checkpoints
A practical model for tasks, microtasks, rendering, and the ordering surprises that appear in production JavaScript.
Abort Signals Are a Composable Cancellation Primitive
How AbortController coordinates fetches, timers, event listeners, and higher-level operations without owning them.
Proxy and Reflect Work Best When You Respect the Invariants
A practical guide to interception, receiver semantics, and the rules a proxy cannot pretend away.
Weak References Are for Memory Relationships, Not Cache Policy
How WeakMap, WeakRef, and FinalizationRegistry interact with reachability and garbage collection.
Structured Clone Is More Than JSON with Better Type Support
What structuredClone preserves, what transfer changes, and where class instances lose their identity.
JavaScript Strings Have Three Useful Notions of Character
How UTF-16 code units, Unicode code points, and grapheme clusters affect indexing and validation.
ES Modules: Live Bindings, Evaluation Order, and Cycles
A closer look at what module loading guarantees—and what changes when the dependency graph contains a loop.
Async Iteration Is a Backpressure Protocol
Why for-await-of is more than convenient syntax, and how it changes the shape of streaming code.
Object Copying Is Really a Property Operation
What spread, Object.assign, descriptors, prototypes, and enumeration order mean for everyday JavaScript objects.