Change #1236718 had a related patch set uploaded (by ATitkov; author: ATitkov):

[mediawiki/extensions/WP25EasterEggs@master] Implement launch banner for Minerva skin

https://gerrit.wikimedia.org/r/1236718

Banner code

<script> 
    const CNContext = mw.centralNotice.kvStore.contexts.GLOBAL;
    const CNBannerKey = 'impression_diet_wp25eastereggs-minerva-launch-banner';
    const impressions = mw.centralNotice.kvStore.getItem( CNBannerKey, CNContext );

    if ( impressions.seenCount === 1 ) {
        mw.loader.using( 'ext.wp25EasterEggs.minervaLaunchBanner', function( require ) {
            require( 'ext.wp25EasterEggs.minervaLaunchBanner')();
        } );
    }
</script>

In order to test locally, one can run the following in the js console

mw.loader.using( 'ext.wp25EasterEggs.minervaLaunchBanner', function( require ) {
    require( 'ext.wp25EasterEggs.minervaLaunchBanner')();
} );

There is still one missing part - the banner is supposed to be displayed only on Minerva

For the banner code above, should the if condition be if ( impressions.seenCount === 0 ) or <1? Just want to double check bc I'm not familiar with Central Notice

The code used for the banner was partially taken from here https://phabricator.wikimedia.org/T361047#9839444 which was setup with "maximum impressions any individual will see" being 2.

So IIUC impressions.seenCount accounts for the current view of the banner by the user, thus having impressions.seenCount === 1 on first view.

There is still one missing part - the banner is supposed to be displayed only on Minerva

The CNB campaign will handle that part

Hi @Ejegg! I have been helping @ATitkov and some others in P&T prepare centralnotice banners to promote the Easter Egg feature they're building.

They're using javascript to display the banner, you can see the banner code a couple comments up. I thought you might be able to answer this one specific question:

Will mw.centralNotice.kvStore.getItem( CNBannerKey, CNContext ); in their code return seenCount 0 or 1 on the first banner impression?

@spatton and @ATitkov that should be 1 by the time any in-banner code gets to read it.

The seenCount is incremented and stored in the 'preBannerHandler':
https://phabricator.wikimedia.org/diffusion/ECNO/browse/wmf_deploy/resources/subscribing/ext.centralNotice.impressionDiet.js#L123

Then the pre-banner hooks are called before the banner code is loaded into the page:
https://phabricator.wikimedia.org/diffusion/ECNO/browse/wmf_deploy/resources/ext.centralNotice.display/index.js#L476

@spatton and @Ejegg thank you for making it clear! Much appreciated!

Change #1236718 merged by jenkins-bot:

[mediawiki/extensions/WP25EasterEggs@master] Implement launch banner for Minerva skin

https://gerrit.wikimedia.org/r/1236718

Change #1240241 had a related patch set uploaded (by ATitkov; author: ATitkov):

[mediawiki/extensions/WP25EasterEggs@master] Remove launch banner for Minerva skin

https://gerrit.wikimedia.org/r/1240241

Thank you @Volker_E for catching!! There is indeed a patch for review 🙃

Tested on enwiki beta with

mw.loader.using( 'ext.wp25EasterEggs.minervaLaunchBanner', function( require ) {
    require( 'ext.wp25EasterEggs.minervaLaunchBanner')();
} );

Testing note to test in production:

• check if a modal is displayed, as per design, not an overlay:

Change #1240241 merged by jenkins-bot:

[mediawiki/extensions/WP25EasterEggs@master] Remove launch banner for Minerva skin

https://gerrit.wikimedia.org/r/1240241

Checked on enwiki beta (with https://gerrit.wikimedia.org/r/c/mediawiki/extensions/WP25EasterEggs/+/1240241) - the mobile centralNotice campaign is not shown.