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Building my first Chrome app and was wondering how to run myscript.js only when icon.png is clicked. Now it just runs whenever a page loads.
Here is my manifest.json file:
{
"name": "My extension",
"version": "1.0",
"background_page": "background.html",
"permissions": [
"tabs", "http://*/*"
],
"content_scripts": [
{
"matches": ["http://*/*"],
"js": ["myscript.js"],
"run_at": "document_end"
}
],
"browser_action": {
"default_icon": "icon.png"
}
}

If you don't need the content script any other time except when the button is pressed, see the Chrome docs on programmatic injection to use executeScript to inject scripts on the fly.

You'll want to look into message passing. Basically the set up is:
Make another content script that listens for instructions
When the popup is clicked, fire instructions off to the content script
Content script does what it needs to do, passes back something that says it's done
Popup knows the work has been done
This is done so content scripts and background scripts' (or popups) are isolated and secure.