Why Promises Are Better Than Callbacks

What is a Callback:

    A callback is a function that is passed as an argument to another function and executed later.

Example:

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

function sayBye() {
  console.log("Bye!");
}

greet("Bala", sayBye);

Output:

Hello Bala
Bye!

What is Callback Hell:

When callbacks are nested inside other callbacks many times, it becomes hard to read and maintain. This is called Callback Hell.

Example:

setTimeout(() => {
  console.log("Step 1");

  setTimeout(() => {
    console.log("Step 2");

    setTimeout(() => {
      console.log("Step 3");

      setTimeout(() => {
        console.log("Step 4");
      }, 1000);

    }, 1000);

  }, 1000);

}, 1000);

This code looks like a pyramid shape.
This is called Callback Hell or Pyramid of Doom.

Problems in Callback Hell:
*Hard to read
*Hard to debug
*Hard to maintain
*Error handling is difficult

What is a Promise:

A Promise is used to handle asynchronous operations in a better way.

A Promise has 3 states:

Pending
Resolved (Success)
Rejected (Error)

Promise Example:

let promise = new Promise(function(resolve, reject) {
  let success = true;

  if (success) {
    resolve("Task completed");
  } else {
    reject("Task failed");
  }
});

promise
  .then(function(result) {
    console.log(result);
  })
  .catch(function(error) {
    console.log(error);
  });

Callback Hell vs Promise:

Callback Hell	Promise
Nested callbacks	Chain using .then()
Hard to read	Easy to read
Hard to maintain	Easy to maintain
Error handling difficult	Error handling easy with .catch()

Promise States Diagram:

Draw a simple flow:

         [Pending]
       /   \
      /     \

[Resolved] Rejected (Error)

              Real-World Example Diagram:

Use a food order example

CallbackHell:

Order Food
↓
Prepare Food
↓
Pack Food
↓
Deliver Food

Promise:

Order → Prepare → Pack → Deliver

You can end your blog like this:

",Callback Hell makes code messy. Promises make code clean, readable, and easy to manage."