open
Sets the request method, request URL, and synchronous flag.
Throws a "SyntaxError" DOMException if either method is not a valid method or url cannot be parsed.
Throws a "SecurityError" DOMException if method is a case-insensitive match for CONNECT
, TRACE
, or TRACK
.
Throws an "InvalidAccessError" DOMException if async is false, current global object is a Window object, and the timeout attribute is not zero or the responseType attribute is not the empty string.