Enter a Word
Event Loops
JavaScript uses an event loop to handle asynchronous function calls.
When a program is run, function calls are made and added to a stack.
The functions that make requests that need to wait for servers to respond
then get sent to a separate queue.
Once the stack has cleared, then the functions in the queue are executed.
Web developers use the event loop to create a smoother browsing experience by
deciding when to call functions and how to handle asynchronous events.
my course explored one system of technologies called
Asynchronous JavaScript and XML, or AJAX.
You can also read the MDN documentation on Event Loops
Here
and you can read an Introduction to XML - an MDN documentation
Here
XHR GET Diagram
Codeacademy have created this image as a basic example of the XHR GET commands
const xhr = new XMLHttpRequest();
the xhr can be called anything but calling it
xhr is the accepted name.
// xhr is the accepted name but can be anything
const xhr = new XMLHttpRequest();
// the url is a string
const url = "https://api-to-call.com/endpoint";
// set this to json as it is how the
// response is going to be formatted
xhr.responseType = "json";
// this property defines a function to be
// executed when the readyState changes.
xhr.onreadystatechange = () => {
// this checks to see if
// the request has finished
if (xhr.readyState === XMLHttpRequest.DONE) {
// return the response property
return xhr.response;
}
};
// open creates a new GET request
xhr.open("GET", url);
// send the request
xhr.send();
// NOTE
// I think that with the xhr.open("GET", ...) the
// xhr.send() will always have no parameter, ie
// just xhr.send()
// BUT
// If using xhr.open("POST", ...); then
// xhr.send() will have a parameter eg
// xhr.send(data);