Someone to ask questions about callback?

Question

How is it really a callback?
Callback is it?

Code:
function exe(callback) {
console.log("test")
callback();
}
function ex() {
console.log("test2")
}
exe(ex);

Answer 1

Yes, in this case `res` is the callback.

Answer 2

Not totally sure what you're asking, but the `exe` function, instead of returning a useful value, calls a function once it's done.
That function is called a callback, or outside of javascript-land, a continuation.

Note that all you are really doing is

console.log("test");
console.log("test2");

So continuation-passing style (cps) is just another way to structure code and you can (*usually) convert between direct style and cps freely.

__
*In javascript it's not that simple because of asynchronous code, like code that runs when you click a button on a web page.
In nodejs you will see callbacks everywhere.

Answer 3

Here's one you might know:

setTimeout(function(){
console.log("Hello!");
}, 2000);

This will print "Hello!" in two seconds. The function you are passing is the callback.

Here's one from nodejs:

fs.readFile("file.txt", (err, data) => {
console.log("file.txt contains:", data);
});

This will execute the callback once nodejs is done reading the file.

Answer 4

Schindlabua so I see well if I understand, because I'm kind of lost kkk, and if I do like this? Can it be considered a callback?

ex:
var param = {
name: 'Doug',
email: '[e-mail]'
};
exe(param, res);

function res(resposta) {
alert(resposta);
}

function exe(para, callback) {
console.log("ok");
data = para.name;
callback(data);
}

Answer 5

Schindlabua can you show me an easy example of a callback, so I'm having trouble understanding?

Answer 6

Schindlabua thank you