Why do we pass null to XMLHttpRequest.send?

Question

Why is send so often called as

xhr.send(null)

instead of

xhr.send()

?

W3, MDN, and M

Answer 1

The XMLHttpRequest.send() method sends the request. If the request is asynchronous (which is the default), this method returns as soon as the request is sent. If the request is synchronous, this method doesn't return until the response has arrived. send() accepts an optional argument for the request body. If the request method is GET or HEAD, the argument is ignored and request body is set to null.