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Dustin Henry7,392 Points
Why do we do xhr.onreadystatechange = function instead of xhr.onreadystatechange(function)?
For instance, if I was adding an Event Handler to a DOM level object, I would do object.addEventListener('click', function), but with the onreadystatechange event handler, an equals sign is used instead. Why is that? Thank you for the help!
Steven Parker228,119 Points
The "addEventListener" method establishes an event handler for an object, but "onreadystatechange" is an event handler.
It might make more sense if we compare two ways of setting up "myClickHandler" on some object:
myButton.addEventListener('click', myClickHandler); // this is one way myButton.onclick = myClickHandler; // this is another
Both of those do (almost) the same thing. The advantage of "addEventListener" is that you can attach more than one handler that way.