Why is chrome.runtime undefined when running JS inside a page from a content script?
google-chrome-extension, javascript
Solution
If you're inserting JavaScript into a page with a `<script>` tag, it executes in the page's context.
Sometimes it is desirable: that's the only way to access page-level JavaScript objects.
But in your case it means that the code does not have access to Chrome APIs, as it is "the same" as the page's code.
You need to look into communicating between page-level and content scripts, or between page-level and background (spoiler, in most cases needs a context script proxy anyway).
Problem
I am creating a Google Chrome extension (my first one) and I want to send messages from the extension to the current tab. I am following the documentation: https://developer.chrome.com/apps/runtime#event-onMessage The extension loads a small external JS into the tab's HTML, which contains the following code: ``` chrome.runtime.onMessage.addListener( function(request, sender, sendResponse) { console.log(request) } ); ``` As soon as the JS is loaded I get the following error: `Uncaught TypeError: Cannot read property 'onMessage' of undefined`. Opening console and typing `chrome`, I can see that the runtime is not a property of `chrome`. It looks like I am doing something wrong, but what? Do I need to add something to the `manifest.json` file? Chrome Version 39.0.2171.71 m Thank you.