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Priority Hints provide developers a way to indicate a resource's relative importance to the browser, allowing more control over the order resources are loaded.
Many factors influence a resource's priority in browsers. These include type, visibility, and preload status of a resource. Priority Hints introduces a developer-set "importance" attribute allowing developers to influence the computed priority of a resource. Supported importance values are auto, low, and high.
Search tagspriority-hints, priority hints
TAG review statusPending
Interoperability and CompatibilityGecko
: No signalWebKit
: No signalWeb developers
: Strongly positive
Goals for experimentation
The goal is to re-start the origin trial experiment for Priority Hints with a focus on some specific use cases that have generated significant developer interest:
The bulk of the experiment will be focused on making sure the API surface meets developers needs and works as expected.
- Boost the priority of the LCP image for a page by specifying importance="high" on the image element, causing LCP to happen sooner.
- Increase the priority of async scripts using better semantics than the current hack that is commonly used (inserting a link preload for the async script)
- Decreasing the priority of late-body scripts to allow for better sequencing with images.
- Decreasing the priority of CSS to allow for sequencing with parser-blocking scripts.
Reason this experiment is being extended
The previous experiment was run before the recent focus on core web vitals and LCP in particular and did not generate as much developer interest as there is now. There were also prioritization issues with preload that are fixed in 95 that made it difficult to experiment with for the script case.
There is pretty significant demand from developers for the knobs that Priority Hints provide, particularly for improving LCP.
Ongoing technical constraints
Will this feature be supported on all six Blink platforms (Windows, Mac, Linux, Chrome OS, Android, and Android WebView)?YesNo
Requires code in //chrome?False
|OriginTrial desktop last||101|
|OriginTrial desktop first||96|
|OriginTrial android last||101|
|OriginTrial android first||96|
Link to entry on the Chrome Platform Statushttps://www.chromestatus.com/feature/5273474901737472
Links to previous Intent discussionsIntent to Experiment: https://groups.google.com/a/chromium.org/g/blink-dev/c/jpeSdM897Xw/m/CY6tothSDgAJ