| # Back/forward cache NotRestoredReasons API |
| |
| Contact: bfcache-dev@chromium.org |
| |
| This document describes the status of the current implementation of the |
| [NotRestoredReasons API](https://github.com/rubberyuzu/bfcache-not-retored-reason/blob/main/NotRestoredReason.md) |
| in Chrome, and how to enable it. |
| |
| Starting from version 108, |
| Chrome experimentally supports NotRestoredReasons API. |
| This allows sites to access what reasons are preventing their pages from |
| being restored from back/forward cache.. |
| |
| Note that this API is not available by default. |
| Chrome plans to do an origin trial |
| to evaluate its effectiveness |
| and to allow site authors to give feedback. |
| |
| ## What’s supported |
| |
| A new field [notRestoredReasons](https://github.com/rubberyuzu/bfcache-not-retored-reason/blob/main/NotRestoredReason.md) is added to |
| performanceNavigationTiming API. |
| This new field will report the reasons that prevented back/forward cache on the page in a frame tree structure. |
| |
| ## Activation |
| |
| The policy can be enabled in several ways. |
| |
| ### Using the Chromium UI |
| |
| Enable the flag chrome://flags/#enable-experimental-web-platform-features . |
| You also have to enable back/forward cache flag via chrome://flags/#back-forward-cache . |
| |
| ### Using Origin Trial |
| |
| The [Origin Trial](https://developer.chrome.com/blog/origin-trials/) feature is named `NotRestoredReasons`. |
| Registration for the trial is [here](https://developer.chrome.com/origintrials/#/view_trial/3101854243351429121). |
| See [feature status](https://chromestatus.com/feature/5760325231050752) to find out |
| if the origin trial is currently running. |
| |
| The [origin trial tutorial](https://developer.chrome.com/docs/web-platform/origin-trials/#take-part-in-an-origin-trial) describes how to participate. |
| |
| ### Verifying the API is working |
| |
| In devtools, run the following piece of javascript after navigating to a page, and clicking back/forward button. |
| |
| ```js |
| performance.getEntriesByType('navigation')[0].notRestoredReasons; |
| ``` |
| |
| If it gives you a value, it succeeds. |
| If it gives `undefined` then the feature is not enabled. |
| |
| ## Related Links |
| |
| - [Chrome Status](https://chromestatus.com/feature/5760325231050752) |
| - [NotRestoredReasons API Explainer](https://github.com/rubberyuzu/bfcache-not-retored-reason/blob/main/NotRestoredReason.md) |
