tools/chrome_extensions/open_my_editor/ext/cs-content.js

// Copyright 2017 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

// For cs.chromium.org

let line = 0;

document.addEventListener('contextmenu', (event) => {
  let element = event.target;
  while (element != null && element.tagName == 'SPAN') {
    if (element.className == 'stx-line') {
      line = parseInt(element.id.split('_')[1]);
      break;
    } else {
      element = element.parentElement;
    }
  }
}, true);

chrome.runtime.onMessage.addListener((request, sender, sendResponse) => {
  if (request == 'getLine') {
    sendResponse({line: line});
    line = 0;
  }
});