wikimedia/mediawiki-core

( function () {
    'use strict';

    function initToc( tocNode ) {
        const toggleNode = tocNode.querySelector( '.toctogglecheckbox' );

        if ( !toggleNode ) {
            return;
        }

        let hidden = false;

        toggleNode.addEventListener( 'change', function () {
            hidden = !hidden;
            mw.cookie.set( 'hidetoc', hidden ? '1' : null );
        } );

        // Initial state
        if ( mw.cookie.get( 'hidetoc' ) === '1' ) {
            toggleNode.checked = true;
            hidden = true;
        }
    }

    mw.hook( 'wikipage.content' ).add( function ( $content ) {
        const tocs = $content[ 0 ] ? $content[ 0 ].querySelectorAll( '.toc' ) : [];
        let i = tocs.length;
        while ( i-- ) {
            initToc( tocs[ i ] );
        }
    } );
}() );