add script

extension.json

@@ -48,6 +48,9 @@
 			"styles": [
 				"styles/ext.networknotice.Notice.less"
 			],
+			"scripts": [
+				"scripts/ext.networknotice.Notice.js"
+			],
 			"position": "bottom"
 		}
 	},

resources/scripts/ext.networknotice.Notice.js

@@ -0,0 +1,56 @@
+( function ( window, document ) {
+	'use strict';
+
+	const LOCAL_STORAGE_KEY = 'networknotice';
+
+	function init() {
+		if ( 'localStorage' in window ) {
+			document.querySelectorAll( '[data-component="network-notice"]' ).forEach( function( notice ) {
+				const key = notice.dataset.id;
+				if ( isInStorage( key ) ) {
+					notice.classList.add( 'd-none' );
+				} else {
+					const closeButton = notice.querySelector(
+						'[data-component="network-notice-close-button"]'
+					);
+					closeButton.onclick = function() {
+						notice.classList.add( 'd-none' );
+						putIntoStorage( key );
+					};
+				}
+			} );
+		}
+	}
+
+	function getItemsFromStorage() {
+		const items = localStorage.getItem( LOCAL_STORAGE_KEY );
+		return items ? JSON.parse( items ) : [ ];
+	}
+
+	function putIntoStorage( key ) {
+		const items = getItemsFromStorage();
+		if ( !items.includes( key ) ) {
+			items.push( key );
+			localStorage.setItem( LOCAL_STORAGE_KEY, JSON.stringify( items ) );
+		}
+	}
+
+	function isInStorage( key ) {
+		const items = getItemsFromStorage();
+		return items.includes( key );
+	}
+
+	/**
+	 * Check on document readyState
+	 */
+	if ( document.readyState === 'complete' ) {
+		init();
+	} else {
+		document.addEventListener( 'readystatechange', () => {
+			if ( document.readyState === 'complete' ) {
+				init();
+			}
+		} );
+	}
+
+} ( window, document ) );

src/Hooks/MainHookHandler.php

@@ -22,6 +22,7 @@ class MainHookHandler implements
 	 */
 	public function onBeforePageDisplay( $out, $skin ): void {
 		$out->addModuleStyles( 'ext.networknotice.Notice' );
+		$out->addModules( 'ext.networknotice.Notice' );
 	}
 
 	/**