Callbacks in Javascript - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a callback function in JavaScript?

A callback function is a function passed into another function as an argument, which is then invoked inside the outer function to complete some kind of action.

beginner

Why do we use callbacks in JavaScript?

Callbacks let us run code after another function finishes, especially for tasks that take time like loading data, so the program doesn’t stop and wait.

beginner

How do you define and use a callback function? Show a simple example.

You define a function and pass it as an argument to another function. For example:<br><pre>function greet(name) {
  console.log('Hello ' + name);
}
function processUserInput(callback) {
  const name = 'Alice';
  callback(name);
}
processUserInput(greet);</pre>

beginner

What problem can callbacks help solve in JavaScript?

Callbacks help manage tasks that take time, like reading files or fetching data, so the program can keep running without waiting and freezing.

intermediate

What is "callback hell" and why should it be avoided?

"Callback hell" happens when callbacks are nested inside callbacks many times, making code hard to read and maintain. It’s better to use promises or async/await to keep code clean.

What is a callback function?

A A function that cannot be called

B A function that returns a value

C A function passed as an argument to another function

D A function that runs only once

A callback is a function passed into another function to be called later.

Why are callbacks useful in JavaScript?

A To stop the program until a task finishes

B To run code after a task finishes without stopping the program

C To make the program run slower

D To create new variables

Callbacks let JavaScript run other code while waiting for tasks like data loading.

Which of these is an example of passing a callback?

A setTimeout(() => console.log('Hi'), 1000)

B let x = 5 + 3

C function add(a, b) { return a + b; }

D console.log('Hello')

setTimeout takes a function as a callback to run after a delay.

What is a common downside of using many nested callbacks?

A Code runs faster

B Code becomes shorter

C Code uses less memory

D Code becomes hard to read and maintain

Many nested callbacks create "callback hell," making code confusing.

Which modern JavaScript feature helps avoid callback hell?

A Promises and async/await

B Global variables

C Loops

D Alerts

Promises and async/await make asynchronous code easier to read and write.

Explain what a callback function is and why it is useful in JavaScript.

Think about how JavaScript runs code that takes time without stopping everything.

Describe what "callback hell" is and how you can avoid it.

Imagine stacking many callbacks inside each other and how that looks.