JavaScript(JS) CallBack

In JavaScript, a callback is a function that is passed as an argument to another function and is called when that function has completed its task. The callback function is executed when the first function is finished, and can be used to handle the result of the operation or to perform additional tasks.

Callbacks are commonly used to handle asynchronous operations, such as fetching data from a server or processing user input. Here is an example of a callback function that is used to handle the result of an asynchronous operation:

function fetchData(url, callback) {
  fetch(url)
    .then(response => response.json())
    .then(data => {
      callback(data);
    })
    .catch(error => {
      console.error(error);
    });
}

function processData(data) {
  console.log(data);
}

fetchData('https://api.example.com/data', processData);

In this example, the fetchData() function takes two arguments: the URL to fetch the data from, and a callback function to handle the data once it is fetched. The fetch() function is used to fetch the data from the specified URL, and the then() method is used to process the response as JSON data. The callback() function is then called with the processed data as an argument.

The processData() function is an example of a callback function that is passed as an argument to fetchData(). It takes the fetched data as an argument and logs it to the console.

Callbacks are an essential part of JavaScript, and are used extensively in modern web development. They allow you to write code that is more responsive and efficient, and are a powerful tool for handling asynchronous operations.