Async JavaScript

Imagine ordering pizza. You don't stand at the door waiting - you give them your phone number (a callback) and they call you when it arrives. That's exactly how callbacks work in JavaScript!

What are callbacks? A callback is a function that runs AFTER something else finishes. It's like saying "when you're done with that, do this next."

Simple example with setTimeout:

setTimeout(function() {

console.log("This runs after 3 seconds");
}, 3000);

Why we need callbacks:

• •Some operations take time (loading data, timers)
• •We don't want to freeze the page while waiting
• •Callbacks let other code run while waiting

Callback pattern:

function doSomethingAsync(callback) {
  // Simulate async operation
  setTimeout(() => {
    const result = "Operation complete!";
    callback(result);
  }, 1000);
}
// Using it:

doSomethingAsync(function(result) {

console.log(result);  // "Operation complete!"
});

The "Callback Hell" problem:

// When you need multiple async operations:

getData(function(a) { getMoreData(a, function(b) { getMoreData(b, function(c) { // This nesting gets messy! }); }); });

Callbacks are the foundation of asynchronous JavaScript, but modern code uses Promises and async/await for cleaner syntax!