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Callback functions in JavaScript are functions that are passed as arguments to other functions and are executed later, often after an asynchronous operation completes or in response to some event. Callback functions are a fundamental concept in JavaScript, especially in asynchronous programming. Here's how they work:

Basic Usage:
In JavaScript, functions are first-class citizens, which means they can be passed around as arguments to other functions.
A callback function is simply a function that is passed as an argument to another function and is executed later.
Example:

Here's a simple example of a callback function passed to the setTimeout function, which executes the callback after a specified delay.

JavaScript code:
function greet() {
console.log("Hello, world!");
}

setTimeout(greet, 1000); // Output: Hello, world! (after 1 second)

Asynchronous Operations:
Callback functions are commonly used with asynchronous operations, such as fetching data from a server, reading files, or handling user input.
The callback function is executed once the asynchronous operation completes, allowing you to handle the result or perform further actions.

JavaScript code
function fetchData(callback) {
setTimeout(function() {
const data = "Some data fetched";
callback(data);
}, 1000);
}

function processData(data) {
console.log("Data received:", data);
}

fetchData(processData); // Output: Data received: Some data fetched (after 1 second)

Anonymous Callback Functions:
Callback functions can also be defined inline as anonymous functions.

JavaScript code:
setTimeout(function() {
console.log("This is an anonymous callback function.");
}, 1000);
Error-First Callbacks:

In Node.js and some JavaScript libraries, it's a common convention to pass callback functions with an error-first argument.

JavaScript code:
function readFile(path, callback) {
// Simulate asynchronous file reading
setTimeout(function() {
const error = null; // No error
const data = "File content";
callback(error, data);
}, 1000);
}

readFile("example.txt", function(error, data) {
if (error) {
console.error("Error:", error);
} else {
console.log("Data:", data);
}
});

Callback functions are a powerful mechanism for handling asynchronous operations and allowing code to be executed in response to events or upon completion of tasks. They are widely used in JavaScript for managing asynchronous behavior and implementing non-blocking code.

Chapter :
00:00 What is Callback Functions
00:20 Basic Usage
00:33 Example - Callback function
00:51 Asynchronous Operations
01:26 Anonymous Callback Functions
01:36 Error-First Callbacks
02:10 Summery


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