Add-ons using the techniques described in this document are considered a legacy technology in Firefox. Don't use these techniques to develop new add-ons. Use WebExtensions instead. If you maintain an add-on which uses the techniques described here, consider migrating it to use WebExtensions.
From Firefox 53 onwards, no new legacy add-ons will be accepted on addons.mozilla.org (AMO).
From Firefox 57 onwards, WebExtensions will be the only supported extension type, and Firefox will not load other types.
Even before Firefox 57, changes coming up in the Firefox platform will break many legacy extensions. These changes include multiprocess Firefox (e10s), sandboxing, and multiple content processes. Legacy extensions that are affected by these changes should migrate to WebExtensions if they can. See the "Compatibility Milestones" document for more.
A wiki page containing resources, migration paths, office hours, and more, is available to help developers transition to the new technologies.
jpm
. The DOM console
object is useful for debugging JavaScript. Because DOM objects aren't available to the main add-on code, the SDK provides its own global console
object with most of the same methods as the DOM console
, including methods to log error, warning, or informational messages. You don't have to require()
anything to get access to the console. It is automatically made available to you.
The console.log()
method prints an informational message:
console.log("Hello World");
Try it out:
- create a new directory, and navigate to it
- execute
jpm init
, accepting all the defaults - open "index.js" and add the line above
- execute
jpm run
Firefox will start, and the following line will appear in the command window you used to execute jpm run
:
info: Hello World!
console
in Content Scripts
You can use the console in content scripts as well as in your main add-on code. The following add-on logs the HTML content of every tab the user loads, by calling console.log()
inside a content script:
require("sdk/tabs").on("ready", function(tab) { tab.attach({ contentScript: "console.log(document.body.innerHTML);" }); });
console
Output
If you are running your add-on from the command line (for example, executing jpm run
or jpm test
) then the console's messages appear in the command shell you used.
If you've installed the add-on in Firefox then the messages appear in Firefox's Browser Console.
But note that by default, calls to console.log()
will not result in any output in the Error Console for any installed add-ons: this includes add-ons installed using the Add-on Builder or using tools like the Extension Auto-installer.
See "Logging Levels" in the console reference documentation for more information on this.
Learning More
For the complete console
API, see its API reference.