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open Method

.NET Framework 3.0

Assigns method, destination URL, and other optional attributes of a pending request.

Syntax

Copy 
object.open(sMethod, sUrl [, bAsync] [, sUser] [, sPassword])

Parameters

sMethod Required. String that specifies the HTTP method used to open the connection: such as GET, POST, or HEAD. This parameter is not case-sensitive.
sUrl Required. String that specifies either the absolute or a relative URL of the XML data or server-side XML Web services.
bAsync Optional. Variant that specifies true for asynchronous operation (the call returns immediately), or false for synchronous operation. If true, assign a callback handler to the onreadystatechange property to determine when the call has completed. If not specified, the default is true.
Performance Note   When bAsync is set to false, send operations are synchronous, and Windows Internet Explorer does not accept input or produce output while send operations are in progress. Therefore, this setting should not be used in situations where it is possible for a user to be waiting on the send operation to complete.
sUser Optional. 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.
sPassword Optional. 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:

Verb / Method Defined In HTTP (RFC-2616) Defined In WebDAV (RFC-2518) Function
GET HTTP WebDAV Request URI
POST HTTP WebDAV Send data to server
HEAD HTTP WebDAV Request URI without body
PUT HTTP WebDAV Store data for URI
DELETE HTTP WebDAV Delete data for URI
MOVE WebDAV Move URI to to new location
PROPFIND WebDAV Request URI Properties
PROPPATCH WebDAV Update or Delete URI Properties
MKCOL WebDAV Create collection at URI
COPY WebDAV Create copy of URI
LOCK WebDAV Create Lock
UNLOCK WebDAV Remove Lock
OPTIONS HTTP WebDAV Request URI Options

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 note Security Alert    Cross-domain, cross-port, and mixed protocol requests are not allowed. The sUrl parameter may only specify 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.

Standards Information

This method is defined in The XMLHttpRequest Object (W3C Working Draft).

Applies To

XMLHttpRequest, XMLHttpRequest Constructor

See Also

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More about security
Ontop of the check the security makes note of, requests to any other protocol than 'http' and 'https' URL's, won't get sent. (Which is requires a work-around when developing an Asynchronous Pluggable Protocol: an IInternetProtocol implementation)
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Misleading secuity note
The security note in this article incorrectly implies that the target of the XMLHTTPRequest object must be XML. This is not correct.
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