Callbacks

A callback is a function passed as an argument to another function, to be called later — either after an operation completes or at a specific time.

1. Basic Callback Example

function greet(name) {
  console.log("Hello, " + name);
}

function processUser(callback) {
  let name = "Alice";
  callback(name);
}

processUser(greet); // "Hello, Alice"

2. Anonymous Callback

setTimeout(function () {
  console.log("Executed after 1 second");
}, 1000);

3. Arrow Function Callback

setTimeout(() => {
  console.log("Arrow callback");
}, 500);

4. Array Method Callbacks

forEach

[1, 2, 3].forEach(num => {
  console.log(num);
});

map

let doubled = [1, 2, 3].map(n => n * 2);

filter

let even = [1, 2, 3, 4].filter(n => n % 2 === 0);

5. Why Use Callbacks?

• Handle asynchronous tasks (API calls, timeouts)
• Reuse logic
• Custom behavior passed into functions

6. Callback Hell (Bad Practice)

Nested callbacks make code hard to read:

doTask1(() => {
  doTask2(() => {
    doTask3(() => {
      console.log("Done");
    });
  });
});

Use Promises or async/await to fix this.