How does JavaScript handle async without threads?
Through Web APIs (setTimeout, fetch, events) that run outside the engine. When done, they queue callbacks. The event loop pushes those callbacks onto the single call stack when it is free.
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More FAQs in Is JavaScript Synchronous or Asynchronous?
JavaScript is synchronous and single-threaded. It executes one statement at a time. Asynchronous behavior comes from the runtime's Web APIs and the event loop, not the language itself.
Because cb goes to the callback queue. The event loop only moves it to the call stack after the current stack is empty and microtasks are done. JS is synchronous, so the timer cannot interrupt running code.
A mechanism that continuously checks if the call stack is empty. If it is, it moves callbacks from the microtask queue (then macrotask queue) onto the stack for execution.
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