Javascript Callback function examples

function checkAge(age, callback) {

  if (age >= 18) {

    callback(true);

  } else {

    callback(false);

  }

}

function allowAccess(isAllowed) {

  if (isAllowed) {

    console.log('Access granted!');

  } else {

    console.log('Access denied!');

  }

}

checkAge(21, allowAccess);

In the example above, the checkAge function takes in an age parameter and a callback function. When the checkAge function is called with an age and a callback function (allowAccess), it checks if the age is greater than or equal to 18. If it is, it calls the callback function with a value of true, and if it isn't, it calls the callback function with a value of false. The allowAccess function then logs either "Access granted!" or "Access denied!" to the console depending on the value of the isAllowed parameter.

function fetchData(callback) { setTimeout(function() { let data = ['apple', 'banana', 'orange']; callback(data); }, 2000); } function displayData(data) { console.log('Fetched data: ' + data.join(', ')); } fetchData(displayData);

In the example above, the fetchData function takes in a callback function. When the fetchData function is called with a callback function (displayData), it simulates an asynchronous operation using setTimeout to wait for 2 seconds before returning an array of data. When the data is returned, the callback function is called with the data as a parameter. The displayData function then logs the fetched data to the console.

let numbers = [1, 2, 3, 4, 5];

let squaredNumbers = numbers.map(function(number) {

  return number * number;

});

console.log(squaredNumbers);

In the example above, the numbers array is mapped to a new array of squared numbers using the map method, which takes in a callback function that is called for each element of the array. The callback function in this case is an anonymous function that takes in a number parameter and returns the square of that number. The squaredNumbers variable then contains the new array of squared numbers, which is logged to the console.

I hope these additional examples help you further understand how callback functions can be used in JavaScript.