HTML, CSS & accessibility
Layouts, forms, browser behavior and accessible interface troubleshooting.
112 troubleshooting guides · Page 4 / 5
Why does a skipped offscreen section cause a jump when it becomes visible?
content-visibility:auto can defer rendering, and an estimated intrinsic size helps reserve space.
How do I stop a fixed header from covering an anchored section title?
Give anchor targets a scroll-margin-top matching the header plus desired spacing, or use scroll-padding on the scrolling container for a broader policy.
How do I stop a modal’s scroll from continuing into the page behind it?
Set an appropriate overscroll-behavior on the modal’s actual scroll container to contain scroll chaining.
Why are report sections missing from printed output when the screen looks correct?
Inspect print styles for overflow containers, fixed heights and hidden content.
Why does break-inside:avoid fail to keep a long report row on one printed page?
Avoid is a fragmentation preference, not a way to fit content taller than the available page.
Why does fetch reach the success path for an HTTP 404 response?
Fetch rejects for network-level failures, but an HTTP error response can still fulfill the promise.
Why does a successful DELETE request fail with Unexpected end of JSON input?
A 204 response has no JSON body.
Why does logging response.text make a later response.json fail?
A response body is a consumable stream.
Why can abort fail response.json after fetch has already resolved?
Fetch can resolve once response headers are available while body reading is still in progress.
Why does mode:no-cors hide my API response instead of fixing CORS?
A no-cors cross-origin response is generally opaque to script, so you cannot read its ordinary status or body as API data.
Why does credentials:include still not send my cross-site session cookie?
Credentials mode is only one part of the decision.
Why did adding a custom header make a previously working cross-origin request fail?
A non-safelisted header can trigger a preflight OPTIONS request.
Why does a multipart upload fail after I set Content-Type manually?
When sending FormData, let the browser generate Content-Type with its matching multipart boundary.
Why does a generated download stop working after I revoke its blob URL?
Revocation releases the URL binding, so revoking before the browser has consumed it can break the action.
Why does replacing image previews gradually increase page memory?
Each createObjectURL call creates a resource binding that should be released when no longer needed.
Why does selecting the same file twice not trigger my upload handler?
The file input may have no value change when the same selection is repeated.
Why does File.text corrupt a legacy Windows-encoded CSV?
File.text decodes as UTF-8.
Why does canvas export throw after drawing a cross-origin image?
Drawing an image without the required origin permission can taint the canvas.
Why does copy-to-clipboard fail when it runs after a delayed request?
Clipboard access depends on a secure context and browser permission or user-activation policy.
Why does an autoplay failure produce an unhandled promise rejection?
play returns a promise that can reject under autoplay policy or media errors.
Why does requestFullscreen fail after awaiting data in a click handler?
Fullscreen requires conditions including transient user activation, and an asynchronous delay can outlive that activation.
Why is a new report tab blocked when I open it after an API call?
Popup policies often require the browsing context to be opened directly from a user gesture.
Why does saving a small preference throw in some browser sessions?
Storage access or writes can fail because of policy, availability or quota.
Why does a localStorage change update other tabs but not the current tab?
The storage event is delivered to other relevant documents, not the document that made the change.
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