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Interview question on event loop

Q1. What is the difference between the call stack and the event loop in JavaScript?​

Ans. The call stack is a data structure that keeps track of the execution context of the currently executing functions, while the event loop is responsible for handling asynchronous operations in a non-blocking way. The call stack is used for synchronous code execution, while the event loop is used for handling callbacks and other asynchronous tasks.

Q2. What is the purpose of the setTimeout function in JavaScript?​

Ans: The setTimeout function is used to delay the execution of a function by a specified number of milliseconds. It is commonly used for performing tasks that need to be executed after a certain amount of time has passed, such as animations, transitions, or polling.

Q3. How does the event loop handle tasks with different priorities?​

Ans. Tasks with different priorities are handled by different task queues. The highest-priority task queue is the microtask queue, which is used for tasks that need to be executed as soon as possible, such as promise callbacks. The next highest-priority queue is the animation frame queue, which is used for tasks that need to be executed before the next repaint, such as animations or transitions. The lowest-priority queue is the task queue, which is used for all other tasks, such as network requests or timer callbacks.

Q4. What is the difference between setInterval and setTimeout functions?​

Ans. The setInterval function is used to repeatedly execute a function at a specified interval, while the setTimeout function is used to delay the execution of a function by a specified amount of time. Both functions are used for scheduling tasks, but setInterval is typically used for tasks that need to be executed at regular intervals, such as polling, while setTimeout is used for one-time tasks, such as animations or transitions.

Q5. What are some common pitfalls to watch out for when working with the event loop?​

Ans. One common pitfall is the risk of creating an infinite loop or a memory leak by repeatedly adding tasks to the event loop without giving it a chance to complete its current tasks. Another pitfall is the risk of blocking the event loop by performing long-running synchronous tasks, which can cause the UI to freeze and become unresponsive. It is important to use asynchronous APIs and optimize code for performance to avoid these issues.