chrome-extensions-samples/functional-samples/sample.sidepanel-dictionary/service-worker.js

// Copyright 2023 Google LLC
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     https://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

function setupContextMenu() {
  chrome.contextMenus.create({
    id: 'define-word',
    title: 'Define',
    contexts: ['selection']
  });
}

chrome.runtime.onInstalled.addListener(() => {
  setupContextMenu();
});

chrome.contextMenus.onClicked.addListener((data) => {
  chrome.runtime.sendMessage({
    name: 'define-word',
    data: { value: data.selectionText }
  });
});