open Method Assigns method, destination URL, and other optional attributes of a pending request.
Syntax
XMLHttpRequest.open(sMethod, sUrl [, bAsync] [, sUser] [, sPassword])[/pre]Parameters
sMethodRequired. String that specifies the HTTP method used to open the connection: such as GET, POST, or HEAD. This parameter is not case-sensitive.
sUrlRequired. String that specifies either the absolute or a relative URL of the XML data or server-side XML Web services.
bAsyncOptional. Variant that specifies true for asynchronous operation (the call returns immediately), or false otherwise. If true, assign a callback handler to the onreadystatechange property to determine when the call has completed. If not specified, the default is true.
sUserOptional. Variant that specifies the name of the user for authentication. If this parameter is null ("") or missing and the site requires authentication, the component displays a logon window.
sPasswordOptional. Variant that specifies the password for authentication. This parameter is ignored if the user parameter is null ("") or missing.
Return Value
No return value.
Remarks
open was introduced in Internet Explorer 7.
The following HTTP verbs and World Wide Web Distributed Authoring and Versioning (WebDAV) methods 
are supported:
GET POST HEAD PUT DELETE MOVE PROPFIND PROPPATCH MKCOL COPY LOCK UNLOCK OPTIONSMicrosoft Internet Explorer caches the results of HTTP GET requests in the Temporary Internet Files (TIF) folder. In most cases, caching improves performance for data that will not change frequently. To guarantee that the results are not cached, use POST.
Security Alert Cross-domain, cross-port, and mixed protocol requests are not allowed. The sUrl parameter may only specify XML data files in the same domain, using the same port and protocol method, as that from which the page is served. Although this method accepts credentials passed via parameter, those credentials are not automatically sent to the server on the first request. The sUser and sPassword parameters are not transmitted unless the server challenges the client for credentials with a 401 - Access Denied response.
After calling this method, use send to send the request and data, if any, to the server.
Applies To
XMLHttpRequest
See Also
abort, onreadystatechange
