User:Enterprisey/talk-tab-count.js

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$( function() {
    if( !document.getElementById( "ca-talk" ) ) return;

    // Insert count early
    var talkTabLink = document.getElementById( "ca-talk" ).childNodes[0].childNodes[0];
    talkTabLink.textContent += " (?)";

    // Determine the name of this page's associated talk page.
    // (If we're already on one, then talkPageName is set to wgPageName.)
    // The " | 1" part is to set the 1's place to a 1, which guarantees a talk namespace.
    var talkPageNamespace = mw.config.get( "wgFormattedNamespaces" )[ mw.config.get( "wgNamespaceNumber" ) | 1 ];
    var talkPageName = talkPageNamespace + ":" + mw.config.get( "wgTitle" );


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

        // 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],
                revisions = data.query.pages[pageid].revisions;

            if( revisions === undefined ) {

                // The talk page does not exist
                talkTabLink.textContent = talkTabLink.textContent.replace( "(?)", "(0)" );
            } else {
                var text = revisions[0]["*"];
                var HEADER_RE = /^\s*==\s*[^=]+?\s*==\s*$/gm;
                var headerMatchList = text.match( HEADER_RE );
                var headerCount = headerMatchList ? headerMatchList.length : 0;
                talkTabLink.textContent = talkTabLink.textContent.replace( "(?)", "(" + headerCount + ")" );
            }
        } );
    } );
} );