DEV Community

XMLHttpRequest in JavaScript

Adam Roynon on March 26, 2020

XMLHttpRequest is an object in JavaScript that allows you to send AJAX requests to the server, it allows you to get a response from the server usin...

Read full post

Artem Tamoian • Mar 26 '20

It's 2020, use promise-based fetch() instead.

Adam Roynon • Mar 26 '20

I agree that you there are better solutions now. It's always good to refresh on the underlying principles and workings though

Artem Tamoian • Mar 27 '20 • Edited

Is using var and non-strict equality (==) a part of refreshing on the underlying principles?

Adam Roynon • Mar 27 '20

Using var is fine for these examples as it is block scoped. I could have use the new let/const keywords plus non-strict equality, etc, etc. But for just showing the basics of XMLHttpRequest they're not needed and it would have over complicated the simple examples.

Artem Tamoian • Mar 27 '20

There's no point in using legacy and problematic syntax such as var and ==. For beginners, it makes sense to show correct examples of modern JavaScript. We don't speak Old Slavonic teaching kids Russian, so why should we use the legacy syntax when teaching people how to code?

Artem Tamoian • Mar 27 '20

The last example is even incorrect, XMLHttpRequest will not do JSON.stringify() automatically for you. Try running this code in the console:

var data = {
  id: 13,
  name: "John Smith",
  age: 34
}

var xhttp = new XMLHttpRequest();

xhttp.onreadystatechange = function() {
  if (this.readyState == 4 && this.status == 200) {
    console.log(this.responseText);
  }
};

xhttp.open("POST", "/addUser", true);
xhttp.send(data);