A callback function is a function that is passed as an argument to another function and is executed after some kind of event. It is essentially a way to make sure certain code does not execute until other code has already finished execution.
For example, let’s say you have a function called “doSomething” that takes two arguments, a number and a callback. The callback is a function that will be called when the doSomething function is finished running:
function doSomething(num, callback) {
// do some work
let result = num * 2;
// call the callback when finished
callback(result);
}
// call doSomething, passing in a number and our callback
doSomething(2, function(result) {
console.log(result); // 4
});