Sometimes it's useful to have a conversation that lasts longer than a single request and response. For information on converting callbacks to promises and for using them in extensions, see our own article. The sendMessage() function's callback will be invoked automatically if no handlers return true or if the sendResponse() callback is garbage-collected.įor information on using promises, see Promises on MDN. If you're using callbacks, the sendResponse() callback is only valid if used synchronously, or if the event handler returns true to indicate that it will respond asynchronously. All other responses to that event will be ignored.įor new extensions you should prefer promises over callbacks. If multiple pages are listening for onMessage events, only the first to call sendResponse() for a particular event will succeed in sending the response. Sending a request from a content script looks like this: You cannot use both a promise and a callback. For backward compatibility, you can alternatively pass a callback as the last argument. To handle the response, use the returned Promise. This lets you send a one-time JSON-serializable message from a content script to the extension, or vice versa. If you only need to send a single message to another part of your extension (and optionally get a response back), use the simplified ndMessage() method or ndMessage() method. That is covered in the cross-extension messages section. It is also possible to send a message to another extension if you know its ID. There is a simple API for one-time requests and a more complex API for long-lived connections to exchange multiple messages within shared context. A message can contain any valid JSON object (null, boolean, number, string, array, or object). Either side can listen for messages sent from the other end, and respond on the same channel. For example, an RSS reader extension might use content scripts to detect the presence of an RSS feed on a page, then notify the background page in order to display a page action icon for that page.Ĭommunication between extensions and their content scripts works by using message passing. The final product for this tutorial is in Commit 4.Since content scripts run in the context of a web page and not the extension, they often need some way of communicating with the rest of the extension. If this is your first time writing a browser extension, congratulations, and I hope you want to go build some more! I definitely recommend checking out the API index for Google Chrome to see the many other kinds of APIs your browser extensions can work with! 🎊 This is because "I'll leave that, and brainstorming other ideas on improving user experience, as a challenge to do I encourage you to keep experimenting with this app and the chrome.tabs API, but for now, we've got a sweet MVP (minimum viable product)! Though one thing you might notice is a little off is that if, say, and are in your top bar, Twitter will come first in the rearranged tabs, even though Google alphabetically comes before Twitter. Reload the extension just one more time in chrome://extensions, click its icon, and your tabs should all now be rearranged in alphabetical order by URL! If you are following along in this tutorial, make a folder titled tab-sorter, put a folder under it called app, and inside the app folder, add the file manifest.json with this
CHROME TABS CODE
A manifest is a JSON file, and it's sort of like "the blueprint of the app", telling you things like what picture to use as your extension's icon, which code the extension runs, and which parts of Chrome the app needs access to, such as web history or bookmarks.
The first thing every browser extension needs is a manifest. It is geared toward people who are getting started with writing browser extensions. This tutorial assumes understanding of the basics of JavaScript, and it's recommended to know about callback functions and the method. That way, if you end up with a whole lot of tabs open from a bunch of different websites, you can use this extension to put all the tabs from the same site together in Chrome's top bar so they're easier to navigate. What I really like about them is that all you need in order to get started building extensions is the stuff you make webpages with, and then by throwing in browser APIs, you can make really useful apps!įor this tutorial, we're going to make a Chrome extension that rearranges the tabs in your browser so they're in order by URL.
In fact, they were my own on-ramp to frontend web development.
Browser extensions are a cool way to build on top of the basic parts of frontend web development: HTML, CSS, and JavaScript.
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