Web Platform · Cluster
JavaScript Runtime
Event loop, jobs, and module execution.
- 01 Task Sources and the Ordering Guarantees of the Event Loop Why the browser runs callbacks from several independent queues, what ordering the specification actually promises, and where cross-queue assumptions break.
- 02 The Microtask Checkpoint and How Promise Jobs Actually Run The mechanics behind promise callbacks: when the job queue drains, how await lowers to a reaction, and why a thenable resolution costs extra turns.
- 03 Rendering Opportunities and When Animation Frame Callbacks Run How the browser decides to paint a frame, what requestAnimationFrame is synchronized to, and why callbacks registered during a frame land in the next one.
- 04 Execution Contexts, Environment Records, and What a Closure Keeps Alive How identifier resolution walks a chain of environment records, why the per-iteration binding of let changes closure behaviour, and which storage a closure pins in memory.
- 05 Object Shapes, Inline Caches, and the Cost of a Polymorphic Site Why property access is fast when objects share a hidden class, how shapes transition, and what turns an inline cache from a lookup into a hash probe.
- 06 Module Linking, Live Bindings, and the Order of Evaluation ECMAScript modules resolve and instantiate the whole graph before running a single statement, which is what makes imports live and cycles behave unlike CommonJS.
- 07 Dynamic Import, Module Maps, and Top-Level Await What import() actually schedules, how the module map keys records by URL, and why top-level await turns a synchronous graph into an asynchronous one.
- 08 Timer Clamping, Background Throttling, and Cooperative Yielding The integer arithmetic and nesting rules behind setTimeout, why intervals do not catch up, and how scheduler priority levels change when a callback runs.
- 09 Structured Clone, Transferables, and the Worker Message Boundary What postMessage copies, what it moves, and where the cost lands: serialization on the sender, deserialization on the receiver, and shared memory behind isolation.
- 10 Realms, Cross-Realm Identity, and Errors That Cross Boundaries Each global object carries its own set of intrinsics, so objects from an iframe or worker fail instanceof checks while remaining fully usable and holding their realm alive.