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Higher-order functions take or return functions — the foundation of map/filter/reduce, pipe/compose, partial application, and currying. With production patterns: API shaping pipelines, middleware, React HOCs, RxJS operators, and async composition.
JavaScript Higher-Order Functions and Composition: pipe() and compose() Read More »
A pure function is deterministic + side-effect-free. Why purity makes code testable, memoizable, parallelizable, and easy to reason about. The functional-core / imperative-shell pattern, immutability, the reference-vs-value trap, and when impurity is OK.
JavaScript Pure Functions and Side Effects: The Gateway to Functional JS Read More »
JavaScript’s iterator protocol (next() returning { value, done }) and Symbol.iterator make for…of work. Generators (function*) build iterators from paused function bodies — lazy sequences, infinite ranges, paginated APIs, and async streams in plain JS.
JavaScript Iterators and Generators: Building Lazy Sequences Read More »
Symbols are JavaScript’s 7th primitive — guaranteed-unique values usable as object keys, hidden from Object.keys/for-in/JSON. Well-known Symbols power iterators, coercion hints, instanceof, and toStringTag. When to use Symbols vs strings.
JavaScript Symbols Explained: The Identifier Type Almost No One Uses Read More »
Three JS inheritance patterns: class extends for true IS-A hierarchies, composition (the default — wins most of the time), and mixins as class factories for orthogonal cross-cutting concerns. When each works, when each hurts, and why “favor composition” is gospel.
JavaScript Inheritance Patterns: Classes vs Composition vs Mixins Read More »
JavaScript is prototype-based wearing a class costume. How [[Prototype]] works, the chain lookup, Object.create vs new, how `class` decompiles to constructor + prototype, super, static methods, and the performance pitfalls of mutating prototypes.
JavaScript Prototypes and the Prototype Chain Explained (with `class` Decoded) Read More »
try/catch only catches synchronous throws inside the try block. Async callbacks, uncaught promises, and event handlers all need different patterns. Custom Error subclasses, the Result type, Error.cause, Promise.allSettled, and the global safety nets you must install.
JavaScript Error Handling Patterns: try/catch, Result Types, and async/await Read More »
WeakMap, WeakSet, and WeakRef let you reference objects without keeping them alive. Restrictions, use cases (DOM annotation, private fields, soft caches, cycle detection), why iteration is forbidden, and why the spec says to use WeakRef sparingly.
JavaScript WeakMap, WeakSet, and WeakRef: When Regular Maps Hold On Forever Read More »
How V8’s generational mark-and-sweep collector actually works, the 4 classic leak patterns in SPAs (forgotten listeners, over-capturing closures, unbounded caches, detached DOM), and how to find a real leak with Chrome DevTools heap snapshot comparison.
JavaScript Memory and Garbage Collection: Why Your SPA Leaks Read More »
Build a Promise from scratch in 60 lines. State machine (pending → fulfilled / rejected), why callbacks run as microtasks, how chaining works (then returns a new Promise that adopts the inner result’s state), catch/finally as sugar, and how async/await desugars to .then.