What is the difference between callback hell and promises in JavaScript?

What is the difference between callback hell and promises in JavaScript?

Callback hell refers to the situation where multiple nested callbacks make code hard to read and maintain. Promises provide a cleaner alternative by allowing asynchronous operations to be handled more elegantly.

Can you give me an example of callback hell?

Sure! Here's a simple example:

function fetchData(callback) {
    getUser(function(user) {
        getPosts(user.id, function(posts) {
            getComments(posts[0].id, function(comments) {
                // Do something with comments
            });
        });
    });
}

How do promises improve this situation?

Promises allow you to chain asynchronous calls, making the code more readable. Here's the same example using promises:

fetchUser()
    .then(user => fetchPosts(user.id))
    .then(posts => fetchComments(posts[0].id))
    .then(comments => {
        // Do something with comments
    });

Are there any downsides to using promises?

While promises are better than callbacks, they can still lead to 'promise chaining' issues if not handled properly. Additionally, error handling can become complex if not managed correctly.