Callback functions are functions that are passed as arguments in other functions. A callback function can then be invoked during the execution of that higher order function (that it is an argument of).

In JavaScript, functions can be passed as arguments because functions are objects.

Suppose there are two functions, functionA() and functionB():

function functionA(num1, num2) {
return num1 + num2;
function functionB(callback) {
return callback(2, 4) * 2;
console.log(functionB(functionA)); // Output: 12

In the code above, functionA() accepts two arguments num1 and num2. The other function, functionB(), accepts a single argument callback. When functionB() is executed, the value of the executed callback argument is returned.

In the log statment, we pass functionA() as the callback to functionB() and 12 is logged to the console.

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