Callback

ELI5 — The Vibe Check

A callback is just a function you pass to another function, saying 'when you're done, call this.' Like giving someone your phone number and saying 'text me when the pizza is ready.' Callbacks were how JavaScript handled async stuff before Promises, which led to the legendary 'callback hell' of deeply nested spaghetti code.

Real Talk

A callback is a function passed as an argument to another function, to be invoked at a later time (synchronously or asynchronously). They are foundational to JavaScript's asynchronous model. Nesting callbacks leads to 'callback hell' (pyramid of doom). Promises and async/await were introduced to address this readability problem.

Show Me The Code

// Simple callback
function greet(name, callback) {
  console.log('Hello, ' + name)
  callback()
}
greet('World', () => console.log('Done!'))

// Callback hell (avoid this)
getUser(id, function(user) {
  getPosts(user.id, function(posts) {
    getComments(posts[0].id, function(comments) {
      // 😱 pyramid of doom
    })
  })
})

When You'll Hear This

Array methods like .map() and .filter() take callbacks.,Callback hell is why Promises were invented.,Event listeners use callbacks: element.addEventListener('click', callback).