#2 Difference between callbacks and promises in javascript

Difference between callbacks and promises in JavaScript: 

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✅ 1. Definition

• Callback:
  • A function passed as an argument to another function, executed after an operation completes.
• Promise:
  • An object that represents the eventual success or failure of an asynchronous operation.

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✅ 2. Syntax

• Callback:
  • Function-based: passed directly into another function.
• Promise:
  • Uses .then() for handling success and .catch() for handling errors.

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✅ 3. Readability

• Callback:
  • Can become messy and hard to read when deeply nested (callback hell).
• Promise:
  • More readable, especially when chaining multiple async operations.

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✅ 4. Error Handling

• Callback:
  • Must handle errors manually at each level (e.g., if (err) return ...).
• Promise:
  • Provides a cleaner .catch() method for centralized error handling.

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✅ 5. Chaining

• Callback:
  • Difficult to chain logically; nesting makes it confusing.
• Promise:
  • Designed for chaining using .then(), making sequences of async actions easier to follow.

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✅ 6. Flexibility

• Callback:
  • Less flexible; control flow is hard to manage when multiple async tasks depend on each other.
• Promise:
  • Offers better control over flow and supports parallel and sequential operations.

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✅ 7. Debugging

• Callback:
  • Debugging is harder due to nested logic and unclear call stacks.
• Promise:
  • Easier to debug because of cleaner and flatter code structure.

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✅ 8. Introduction

• Callback:
  • Native to JavaScript since the beginning.
• Promise:
  • Introduced in ES6 (2015) to solve callback-related problems.

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✅ 9. Example

✅ Callback:

function fetchData(callback) {
  setTimeout(() => {
    callback(null, "Data loaded");
  }, 1000);
}

fetchData((err, data) => {
  if (err) console.error(err);
  else console.log(data);
});

✅ Promise:

function fetchData() {
  return new Promise((resolve, reject) => {
    setTimeout(() => {
      resolve("Data loaded");
    }, 1000);
  });
}

fetchData()
  .then(data => console.log(data))
  .catch(err => console.error(err));

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In Summary:

• Use callbacks for simple async tasks.
• Use promises for better structure, readability, and robust error handling in modern JavaScript.