User:Enterprisey/talk-tab-count.js

Code that you insert on this page could contain malicious content capable of compromising your account. If you import a script from another page with "importScript", "mw.loader.load", "iusc", or "lusc", take note that this causes you to dynamically load a remote script, which could be changed by others. Editors are responsible for all edits and actions they perform, including by scripts. User scripts are not centrally supported and may malfunction or become inoperable due to software changes. A guide to help you find broken scripts is available. If you are unsure whether code you are adding to this page is safe, you can ask at the appropriate village pump.
This code will be executed when previewing this page.

This user script seems to have a documentation page at User:Enterprisey/talk-tab-count.

Note: After saving, you have to bypass your browser's cache to see the changes. Google Chrome, Firefox, Microsoft Edge and Safari: Hold down the ⇧ Shift key and click the Reload toolbar button. For details and instructions about other browsers, see Wikipedia:Bypass your cache.

$( function() {
    mw.loader.using( [ "mediawiki.api" ] ).then( function () {

        // Determine the name of this page's associated talk page.
        // (If we're already on one, then talkPageName is set to wgPageName.)
        var talkPageName;
        var currNamespaceNum = mw.config.get( "wgNamespaceNumber" );
        if( currNamespaceNum % 2 === 0 ) {
            talkPageName = mw.config.get( "wgFormattedNamespaces" )[ currNamespaceNum + 1 ] +
                ":" + mw.config.get( "wgTitle" );
        } else {
            talkPageName = mw.config.get( "wgPageName" );
        }

        // Get the text of the talk page and count the level-2 headers
        ( new mw.Api() ).get( {
            prop: 'revisions',
            rvprop: 'content',
            rvlimit: 1,
            titles: talkPageName
        } ).done( function ( data ) {
            if ( !data.query || !data.query.pages ) return;
            var pageid = Object.getOwnPropertyNames( data.query.pages )[0],
                text = data.query.pages[pageid].revisions[0]["*"];
            var HEADER_RE = /^\s*==(=*)\s*(.+?)\s*\1==\s*$/gm;
            var headerCount = text.match( HEADER_RE ).length;

            // Insert this count into the talk page tab
            var talkTab = document.getElementById( "ca-talk" );
            var countEl = document.createElement( "span" );
            countEl.style.cssText = "color: blue";
            countEl.textContent = headerCount;
            talkTab.childNodes[0].appendChild( countEl );
        } );
    } );
} );