brandonhilkert brandonhilkert - 3 months ago 57
Javascript Question

Chrome Extension - Get DOM content

I'm trying to access the activeTab DOM content from my popup. Here is my manifest:

{
"manifest_version": 2,

"name": "Test",
"description": "Test script",
"version": "0.1",

"permissions": [
"activeTab",
"https://api.domain.com/"
],

"background": {
"scripts": ["background.js"],
"persistent": false
},
"content_security_policy": "script-src 'self' 'unsafe-eval'; object-src 'self'",

"browser_action": {
"default_icon": "icon.png",
"default_title": "Chrome Extension test",
"default_popup": "index.html"
}
}


I'm really confused whether background scripts (event pages with persistence: false) or content_scripts are the way to go. I've read all the documentation and other SO posts and it still makes no sense to me.

Can someone explain why I might use one over the other.

Here is the background.js that I've been trying:

chrome.extension.onMessage.addListener(
function(request, sender, sendResponse) {
// LOG THE CONTENTS HERE
console.log(request.content);
}
);


And I'm just executing this from the popup console:

chrome.tabs.getSelected(null, function(tab) {
chrome.tabs.sendMessage(tab.id, { }, function(response) {
console.log(response);
});
});


I'm getting:

Port: Could not establish connection. Receiving end does not exist.


UPDATE:

{
"manifest_version": 2,

"name": "test",
"description": "test",
"version": "0.1",

"permissions": [
"tabs",
"activeTab",
"https://api.domain.com/"
],

"content_scripts": [
{
"matches": ["<all_urls>"],
"js": ["content.js"]
}
],

"content_security_policy": "script-src 'self' 'unsafe-eval'; object-src 'self'",

"browser_action": {
"default_icon": "icon.png",
"default_title": "Test",
"default_popup": "index.html"
}
}


content.js

chrome.extension.onMessage.addListener(
function(request, sender, sendResponse) {
if (request.text && (request.text == "getDOM")) {
sendResponse({ dom: document.body.innertHTML });
}
}
);


popup.html

chrome.tabs.getSelected(null, function(tab) {
chrome.tabs.sendMessage(tab.id, { action: "getDOM" }, function(response) {
console.log(response);
});
});


When I run it, I still get the same error:

undefined
Port: Could not establish connection. Receiving end does not exist. lastError:30
undefined

Answer

It is quite clear that the terms "background page", "popup", "content script" are still causing you great confusion, so I strongly suggest a more in-depth look at the Google Chrome Extensions Documentation.

I am not going to get into any detail regarding what you have been doing wrong (it's quite a few things). Regarding your question if content scripts or background pages are the way to go:

Content scripts: Definitely
Content scripts are definitely necessary, since they are the only component of an extension that has access to the web-page's DOM.

Background page / Popup: Maybe (probably max. 1 of the two)
Depending on what you are trying to achieve, you might need to have the content script pass the DOM content to either a background page or the popup for further processing.


Let me repeat that I strongly recommend a more careful study of the available documentation !
That said, here is a sample extension that retrieves the DOM content on StackOverflow pages and sends it to the background page, which in turn prints it in the console:

background.js:

// Regex-pattern to check URLs against. 
// It matches URLs like: http[s]://[...]stackoverflow.com[...]
var urlRegex = /^https?:\/\/(?:[^./?#]+\.)?stackoverflow\.com/;

// A function to use as callback
function doStuffWithDom(domContent) {
    console.log('I received the following DOM content:\n' + domContent);
}

// When the browser-action button is clicked...
chrome.browserAction.onClicked.addListener(function (tab) {
    // ...check the URL of the active tab against our pattern and...
    if (urlRegex.test(tab.url)) {
        // ...if it matches, send a message specifying a callback too
        chrome.tabs.sendMessage(tab.id, {text: 'report_back'}, doStuffWithDom);
    }
});

content.js:

// Listen for messages
chrome.runtime.onMessage.addListener(function (msg, sender, sendResponse) {
    // If the received message has the expected format...
    if (msg.text === 'report_back') {
        // Call the specified callback, passing
        // the web-page's DOM content as argument
        sendResponse(document.all[0].outerHTML);
    }
});

manifest.json:

{
  "manifest_version": 2,
  "name": "Test Extension",
  "version": "0.0",
  ...

  "background": {
    "persistent": false,
    "scripts": ["background.js"]
  },
  "content_scripts": [{
    "matches": ["*://*.stackoverflow.com/*"],
    "js": ["content.js"]
  }],
  "browser_action": {
    "default_title": "Test Extension"
  },

  "permissions": ["activeTab"]
}
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