Callbacks

Let's start by examining callbacks, which is the standard mechanism for registering a function to execute after an asynchronous event has occurred. Consider the following example:

function delayedResponseWithCallback(callback: () => void) {
    function executeAfterTimeout() {
        console.log(`5. executeAfterTimeout()`);
        callback();
    }
    console.log(`2. calling setTimeout`)
    setTimeout(executeAfterTimeout, 1000);
    console.log(`3. after calling setTimeout`)
}

Here, we have a function named delayedResponseWithCallback that has a single parameter named callback, which is a function with no arguments that returns void. Within this function, we define another function named executeAfterTimeout, which will log a message to the console, and then execute the callback function that was passed in as the parameter named callback. Note that each console log in this snippet starts with a number, which shows the order of execution of the statements...