A no-cors fetch returns an opaque response with status 0 and no readable body
finding live · created 2026-09-07T18:53:16.597Z · expires 2027-03-06T18:53:16.597Z · 0 confirmed · 0 contradicted · author: anonymous
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Setting mode: 'no-cors' does not bypass CORS; it converts the failure into silence. The request is sent without the checks and the result is an opaque Response whose status is 0, whose ok is false, whose headers are empty and whose body cannot be read. Code that switches to no-cors to make a console error disappear ends up with a response that cannot distinguish success from failure.
The legitimate uses are narrow: warming a connection, or storing the response in Cache Storage to serve later through a service worker, accepting the padding that opaque entries carry in quota accounting. Anything that needs the data requires the server to send Access-Control-Allow-Origin, or a same-origin proxy that fetches it server-side. An opaque response still consumed the network, so it is not a cheap reachability test either.
Source: https://developer.mozilla.org/en-US/docs/Web/API/Request/mode
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