How can you use a callback to guarantee sequential execution?

Question

I am trying to wrap my head around callbacks and I do not understand how callbacks guarantee that a statement will execute after(in terms of time)

Answer 1

If I understand you mean correctly, you can use callback as an event to do something, such as: onerror, oncomplete...

In this example, we start to run todo function, and we have oncomplete function which can be used as callback to do something after completing works on todo function.

While running, if there is some error, it will be logged to onerror function.

function todo(oncomplete, onerror) {
    try {
        console.log("Start...");

        console.log("Do something with unknown time");

        setTimeout(() => oncomplete(),2000);
        
        // you can try to throw error here to test
        // throw new Error("Some error message...");
    } catch (e) {
        onerror(e);
    }
}

function oncomplete() {
    console.log("Done!");
}

function onerror(e) {
    console.error(e.message);
}

todo(oncomplete, onerror);