How do you avoid forgetting to clear timers in JavaScript?
Always store the timer ID and call clearTimeout or clearInterval when done. In React, clean up in useEffect: return () => clearInterval(id). In component-based frameworks, clean up when the component unmounts.
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More FAQs in setTimeout Pitfalls and How to Avoid Them in JavaScript
Expecting exact timing, lost this binding, the closure loop bug (var vs let), forgetting to clear timers, passing arguments incorrectly (calling instead of passing), blocking the stack, and background tab throttling.
Use .bind(obj) to permanently bind this, or wrap the method call in an arrow function (() => obj.method()). Arrows inherit this lexically, so they preserve the correct binding.
Because console.log('hi') is called immediately (it returns undefined), and undefined is passed to setTimeout. Fix by passing the function reference: setTimeout(() => console.log('hi'), 1000) or setTimeout(console.log, 1000, 'hi').
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