Request: mode property
The mode read-only property of the Request
interface contains the mode of the request (e.g., cors,
no-cors, same-origin, or navigate.) This is used
to determine if cross-origin requests lead to valid responses, and which properties of the response are readable.
To construct a request with a specific mode, pass the desired value as the RequestInit option to the Request.Request() constructor.
Note that setting particular modes, especially no-cors, places restrictions on the request methods and headers that may be used, and prevents JavaScript from accessing the response headers or body. See the documentation for RequestInit for more details.
Value
One of the following values:
-
same-origin- : Disallows cross-origin requests. If a request is made to another origin with this mode set, the result is an error.
-
no-cors- : Disables CORS for cross-origin requests. The response is opaque, meaning that its headers and body are not available to JavaScript.
-
cors- : If the request is cross-origin then it will use the Cross-Origin Resource Sharing (CORS) mechanism.
-
navigate- : A mode for supporting navigation. The
navigatevalue is intended to be used only by HTML navigation. A navigate request is created only while navigating between documents.
- : A mode for supporting navigation. The
Default mode
Requests can be initiated in a variety of ways, and the mode for a request depends on the particular means by which it was initiated.
For example, when a Request object is created using the
Request() constructor, the value of the mode property
for that Request is set to cors.
However, for requests created other than by the Request()
constructor, no-cors is typically used as the mode; for example, for
embedded resources where the request is initiated from markup, unless the
crossorigin
attribute is present, the request is in most cases made using the no-cors
mode — that is, for the link or script elements
(except when used with modules), or img, audio,
video, object, embed, or
iframe elements.
Examples
In the following snippet, we create a new request using the Request() constructor (for an image file in the same directory as the script), then save the request mode in a variable:
const myRequest = new Request("flowers.jpg");
const myMode = myRequest.mode; // returns "cors" by default