Intent to Experiment | Deprecation Trial For Disallowing Sync XHR in Page Dismissal

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Katie Dillon

Sep 3, 2019, 12:02:16 PM9/3/19
to blink-dev

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Disallow Sync XHR during page dismissal when the page is being navigated away or closed by the user, this involves the following events (when fired on the path of page dismissal) i.e. beforeunload, unload, pagehide and visibilitychange.

Link to “Intent to Implement” blink-dev discussion

The intent to implement and ship deprecation is here.

Goals for experimentation

Give sites a way to have more time to migrate while allowing us to turn off the feature as planned in M78.

Experimental timeline

The experiment will start in M78 when the feature ships and tentatively go through M86.  

Any risks when the experiment finishes?

After the origin trial expires any sites that continue to use synchronous xhr in page dismissal will break.

Ongoing technical constraints



Use of this feature is reported in the DevTools console.

Will this feature be supported on all five Blink platforms supported by Origin Trials (Windows, Mac, Linux, Chrome OS, and Android)?


Link to entry on the feature dashboard

Chromestatus entry is here.

Ojan Vafai

Sep 5, 2019, 2:51:23 PM9/5/19
to Katie Dillon, blink-dev

This gives sites a (temporary) opt-out for a feature we're already tried deprecating where we don't know of any sites that need the opt-out and it's just a defensive measure to ensure sites have time to manage a transition in case we missed anything the last time this went to stable.

On Tue, Sep 3, 2019 at 9:02 AM Katie Dillon <> wrote:

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