Chrome extension: Execute background page only once when chrome starts

Question

I am playing with chrome extensions, my manifest loads a background page with:

...
"background": { "scripts": ["background_page.js"], "persistent": false },
...

The .js code looks like this:

var once = false;
window.addEventListener("load", function () {
  if ( once == true ) { return; }
  alert( 'test' );
  once = true;
}, false);

This seems to works fine, but i want to run the background_page.js code only once every time the browser starts.

Right now, I am not sure why, but the code is executed more than once. At first I thought it was being executed every time I open a new tab but that's not the case. The alert does appear once I start the browser, then if I open a new tab quickly the alert wont appear, but if I wait about 1 minute or so and open a new tab then the alert appears again.

How can i make sure the background_page.js code runs only once every time the browser starts?

Answer 1

What you are using is an Event Page(background_page.js). Event pages are unloaded when the browser detects that the page is not doing anything. So what's happening is that when you open a new tab, the Event page is being reloaded and starts executing from the top again. This way chrome is able to have your app use less memory and speed up the browser.

If you want to fix the problem simply use persistent:true which will make sure the page "persists" indefinitely or until the user closes the browser. If you would really like to keep your app efficient with memory, you should take a look at the runtime.onSuspend method which gets called each time your Event page unloads. This way you can save stuff before the page gets unloaded so that you can resume where you left off.