Get Text From DOM object. Chrome Extension - google-chrome

Question

I have page https://somepage in internet. Here is part of it's code from chrome code:
..............
<div class="wr">
<div class="auth_username">tesеDom#mail.com</div>
<div class="auth_stars">
<i class="fa fa-star-o fa-fw">
...........................
I have seen many answers and examples, but my code still not working. Seems I am missing something. My manifest:
{
"manifest_version": 2,
"name": "Bot_copy",
"version": "1.0",
"content_security_policy": "script-src 'self' 'unsafe-eval'; object-src 'self'",
"icons": {
"48": "48x48.png",
"128": "128x128.png"
},
"content_scripts": [{
"matches": [ "https://mypage.my" ],
"js": ["helloWorld.js"]
}],
"permissions": [
"activeTab",
"alarms",
"clipboardRead",
"clipboardWrite",
"bookmarks",
"contextMenus",
"contentSettings",
"downloads",
"history",
"nativeMessaging",
"browsingData",
"proxy",
"webRequest",
"webRequestBlocking",
"cookies",
"tabs",
"webNavigation",
"storage",
"tabCapture",
"notifications",
"http://*/",
"https://*/",
"<all_urls>",
"unlimitedStorage",
"debugger"
],
"browser_action": {
"default_title": "Open"
},
"background": {
"scripts": ["background.js"]
}
}
content script
window.onload = function() {
sendMessage();
}
chrome.runtime.onMessage.addListener(function(request, sender, sendResponse) {
sendResponse({
response: "Message received"
});
});
//Send message to background page
function sendMessage() {
//Construct & send message
chrome.runtime.sendMessage({
whattodo:"get_authname"
}, function(response) {
});
}
background
chrome.runtime.onMessage.addListener(
function(request, sender, sendResponse) {
var name = document.getElementsByClassName('auth_username').value;
alert(name);
sendResponse({
response: "Message received"
});
}
);
I received alert "undefined".
Have no idea. Really strange there are no properly documentation I don't understand object document.
Seems I miss how to use documentc object. I tried also document.getElementsByTagName('auth_username'), but it also not working. Which way is correct?

Answer 1

You can not access DOM from background script. You can access DOM from content script only. so try to place following code:
var name = document.getElementsByClassName('auth_username').value;
alert(name);
in contentscript and it works.