Content script code is not being executed - google-chrome

Question

I've taken a look at other related SO posts and the solutions haven't helped solve my issue. This is my first chrome extension, so please bear with me!
I'm writing a simple chrome extension that searches for user provided keywords on a webpage. I can't get the content script that returns the DOM content to run. Some of the code, I've taken from an answer in another SO post, but I can't seem to get it to work for me.
I put a console.log("hello world") at the top of the file, and it doesn't show up, so I think it might be the structure of my project.
manifest.json
{
"name": "keyword search",
"version": "0.0.1",
"manifest_version": 2,
"permissions": [ "tabs" , "storage", "activeTab", "<all_urls>"],
"browser_action": {
"default_popup": "html/form.html"
},
"content_scripts": [{
"matches": [ "<all_urls>" ],
"js": [ "js/jquery.min.js", "content_scripts/content_script.js" ]
}],
"homepage_url": "http://google.com/"
}
js/popup.js
function run() {
running = true;
console.log('running');
var url = "https://www.stackoverflow.com/"
// Get KW & category for search
chrome.storage.local.get(["kw"],
function (data) {
kw = data.kw;
console.log("redirecting to find kw: " + kw);
// Send current tab to url
chrome.tabs.query({active: true, currentWindow: true}, function(tabs) {
chrome.tabs.update(tabs[0].id, {url: url});
chrome.tabs.sendMessage(tabs[0].id, {type: 'DOM_request'}, searchDOM);
});
}
);
}
function searchDOM(domContent) {
console.log("beginning dom search \n" + domContent);
}
content_scripts/content_script.js
// Listen for messages
console.log("hello world")
chrome.runtime.onMessageExternal.addListener(function (msg, sender, sendResponse) {
// If the received message has the expected format...
if (msg.type === 'DOM_request') {
// Call the specified callback, passing
// the web-page's DOM content as argument
sendResponse(document.all[0].outerHTML);
}
});
console
running
redirecting to find kw: TestKeyword
beginning dom search
undefined

Answer 1

First, onMessageExternal is the wrong event (it's for external messaging):
you should use the standard onMessage.
Second, chrome extensions API is asynchronous so it only registers a job, returns immediately to continue to the next statement in your code without waiting for the job to complete:
chrome.tabs.update enqueues a navigation to a new URL
chrome.tabs.sendMessage enqueues a message sending job
the current page context in the tab gets destroyed along with the running content scripts
the tab starts loading the new URL
the message is delivered into the tab but there are no listeners,
but this step may instead run right after step 2 depending on various factors so the content script running in the old page will receive it which is not what you want
the tab loads the served HTML and emits a DOMContentLoaded event
your content scripts run shortly after that because of the default "run_at": "document_idle"
There are at least three methods to properly time it all:
make your content script emit a message and add an onMessage listener in the popup
use chrome.tabs.onUpdated to wait for the tab to load
use chrome.tabs.onUpdated + chrome.tabs.executeScript to simplify the entire thing
Let's take the executeScript approach.
remove "content_scripts" from manifest.json
instead of chrome.tabs.query (it's not needed) use the following:
chrome.tabs.update({url}, tab => {
chrome.tabs.onUpdated.addListener(function onUpdated(tabId, change, updatedTab) {
if (tabId === tab.id && change.status === 'complete') {
chrome.tabs.onUpdated.removeListener(onUpdated);
chrome.tabs.executeScript(tab.id, {
code: 'document.documentElement.innerHTML',
}, results => {
searchDOM(results[0]);
});
}
});
});