setTimeout and clearTimeout in Node.js - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does setTimeout do in Node.js?

setTimeout schedules a function to run once after a specified delay in milliseconds.

beginner

How do you stop a scheduled setTimeout before it runs?

You use clearTimeout with the timer ID returned by setTimeout to cancel the scheduled function.

intermediate

What type of value does setTimeout return in Node.js?

It returns a Timeout object that represents the timer. This object is used to clear the timer if needed.

intermediate

Why might you want to use clearTimeout in your code?

To prevent a scheduled function from running if the condition changes or the task is no longer needed, saving resources and avoiding unwanted actions.

advanced

What happens if you call clearTimeout with an invalid or already cleared timer ID?

Nothing happens; clearTimeout safely ignores invalid or already cleared timers without errors.

What does setTimeout(() => console.log('Hi'), 1000) do?

A Prints 'Hi' after 1 second

B Never prints 'Hi'

C Prints 'Hi' every second

D Prints 'Hi' immediately

setTimeout runs the function once after the delay, so it prints 'Hi' after 1 second.

Which function cancels a scheduled setTimeout?

A removeTimeout()

B cancelTimeout()

C stopTimeout()

D clearTimeout()

clearTimeout() is the correct function to cancel a timer set by setTimeout.

What do you need to keep to cancel a timeout later?

A The function passed to <code>setTimeout</code>

B The timer ID returned by <code>setTimeout</code>

C The delay time in milliseconds

D Nothing, you cannot cancel a timeout

You must keep the timer ID returned by setTimeout to call clearTimeout and cancel it.

If you call clearTimeout twice on the same timer ID, what happens?

A The timer is cleared once, second call does nothing

B An error is thrown

C The timer restarts

D The timer runs immediately

Calling clearTimeout multiple times on the same timer ID is safe; only the first call clears it.

Which of these is true about setTimeout in Node.js?

A It runs the function repeatedly every delay interval

B It blocks the program until the function runs

C It schedules a function to run asynchronously after a delay

D It immediately runs the function and ignores the delay

setTimeout schedules the function to run asynchronously once after the delay.

Explain how you would use setTimeout and clearTimeout together in a Node.js program.

Think about scheduling a task and then stopping it if needed.

Describe what happens if you do not call clearTimeout on a timer you no longer need.

Consider what happens if a delayed task runs unexpectedly.