I have small question with developing an Chrome extension.

How can I get a content of page and find a string after it has been loaded?

As a test i prepared something like this:

chrome.tabs.onUpdated.addListener( function (tabId, changeInfo, tab) {
  if (changeInfo.status == 'complete') 
  {
    if (document.body.innerHTML.indexof("text to find in HTML") !== -1) 
        {
            console.log("found");
        } 
  }

Manifest V3 shows that it is "server-side" scripting so i can't access to document and i don't know what to do now.

ReferenceError: document is not defined at <URL.>