Capturing a Paste Event in Firefox

Imagine yourself building a web app that supports image uploads by simply capturing your computer’s paste keyboard shortcut. Sites like imgur.com already support this behavior and it adds an extra level of convenience for what would otherwise require several additional button clicks.

The paste event has been supported in major browsers for some time now, but interestingly Firefox doesn’t trigger the event unless the user’s cursor is currently focussed in an editable region. This seems to be contradictory to the specification itself, which states:

The paste event has no default action in a non-editable context, but the event fires regardless.

There is an open ticket on Bugzilla related to this behavior, while others have resorted to tricks to move the user’s cursor when detecting that a combination of the “control” and “v” keys are pressed.

In my testing, however, I found that the mere presence of a contenteditable element at the root of the page was sufficient in allowing the paste event to trigger normally in Firefox, even if the element is hidden using display: none; styles.

Check it out in the demo below:

In Firefox (v40.0.3 as of today), you’ll find that the paste event is captured so long as the contenteditable attribute is assigned. When toggling the contenteditable off, thereby removing the attribute, the paste is no longer captured. Admittedly, it’s a nuisance to include this unused element, but it’s certainly an improvement over redirecting or otherwise faking the paste interaction using one of the aforementioned tricks.

While there are many other browser inconsistencies to account for when working with the paste event, I was surprised to find that despite what I had read, it was easier than I had anticipated to capture page-wide pastes in Firefox.