Lib: fix onbeforeunload handler breaking navigation (#1436) #2159
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Lib: fix onbeforeunload handler breaking navigation (#1436) #2159
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All modern browsers show a confirmation dialog when the beforeunload handler returns any value other than null or undefined. Dom.handler returned Js._true as the JS value true, which incorrectly triggered the dialog even when the handler intended to allow navigation. Fix by detecting beforeunload events at runtime in Dom.handler and Dom.full_handler: Js._true returns undefined to JS (allowing navigation without a dialog), while Js._false continues to call preventDefault and also sets event.returnValue for legacy browsers. Dom.invoke_handler normalizes undefined back to Js._true. Also adds Dom.beforeUnloadEvent and Dom_html.beforeUnloadEvent class types with the returnValue property, and types onbeforeunload to use beforeUnloadEvent instead of the generic event type. Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
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@TyOverby, this PR breaks some virtual_dom tests. Can you comment maybe ? |
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@vouillon, any though ? |
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Summary
Fixes #1436.
Dom.handlerconverts the OCamlbool treturn value to a JavaScript return value. When abeforeunloadhandler returnsJs._true(allow navigation), the JS valuetrueis passed to the browser. Modern browsers interpret any non-null, non-undefined return value from abeforeunloadhandler as a request to show the "Leave page?" confirmation dialog. This means that even when the OCaml handler intended to allow navigation, the browser would show a blocking dialog.Changes
The fix detects
beforeunloadevents at runtime inDom.handlerandDom.full_handler:Js._true(allow navigation), returnundefinedto the browser instead oftrue, so no dialog is shown.Js._false(block navigation), also setevent.returnValue = ""for legacy browser compatibility.Dom.invoke_handler, normalizeundefinedback toJs._trueso callers that chain handlers still see a properbool tvalue.Also adds
Dom.beforeUnloadEventandDom_html.beforeUnloadEventclass types with thereturnValueproperty, and typesonbeforeunloadto usebeforeUnloadEventinstead of the genericeventtype.