Welcome to the Treehouse Community

Want to collaborate on code errors? Have bugs you need feedback on? Looking for an extra set of eyes on your latest project? Get support with fellow developers, designers, and programmers of all backgrounds and skill levels here with the Treehouse Community! While you're at it, check out some resources Treehouse students have shared here.

Looking to learn something new?

Treehouse offers a seven day free trial for new students. Get access to thousands of hours of content and join thousands of Treehouse students and alumni in the community today.

Start your free trial

JavaScript AJAX Basics (retiring) AJAX Concepts A Simple AJAX Example

Mayank Munjal
seal-mask
.a{fill-rule:evenodd;}techdegree seal-36
Mayank Munjal
Front End Web Development Techdegree Graduate 18,120 Points
Posted by Mayank Munjal
.a{fill-rule:evenodd;}techdegree seal-36
Mayank Munjal
Front End Web Development Techdegree Graduate 18,120 Points

So xhr.onreadystangechange is the callback function but I'm getting confused as to when it is called back?

I don't see a higher order function using the callback function as an argument so if someone can explain what's going on, it will help a lot!

1 Answer

Steven Parker
Steven Parker
231,275 Points
Steven Parker
Steven Parker
231,275 Points

The callback function is used by an internal event handler that is established by the "xhr.send()" call. It accesses the callback directly as a property of the "xhr" object instead of having it passed as an argument.