An example of a callback hell

simple callback hell.js

/*
Suppose I want to add two numbers, then double it, then square that number, then add double it again.
 */
addTwoNos(2, 3, (sum) => {
    double(sum, (doubleOfSum) => {
        square(doubleOfSum, (square) => {
            double(square, (doubleOfSquare) => {
                console.log(doubleOfSquare)
            })
        })
    })
});  // outputs result of (((2+3)*2)^2)*2 which is 200


function addTwoNos(num1, num2, callback) {

    callback(num1 + num2)
}

function double(num, callback) {

    callback(num * 2)

}

function square(num, callback) {

    callback(num * num)

}