2 min read

Earlier this month, Mozilla announced a fancy new feature called “Time Travel debugging” for its Firefox Nightly web browser at the JSConf EU 2018.  With time travel debugging, you can easily track the bugs in your code or app as it lets you pause and rewind to the exact time when your app broke down.

Time travel debugging technology is particularly useful for local web development where it allows you to pause and step forward or backward, pause and rewind to a previous state, rewind to the time a console message was logged and rewind to the time where an element had a certain style. It is also great for times where you might want to save user recordings or view a test recording when the testing fails.

With time travel debugging, you can record a tab on your browser and later replay it using WebReplay, an experimental project which allows you to record, rewind and replay the processes for the web.

According to Jason Laster, a Senior Software Engineer at Mozilla,“ with time travel, we have a full recording of time, you can jump to any point in the path and see it immediately, you don’t have to refresh or re-click or pause or look at logs”.

Here’s a video of Jason Laster talking about the potential of time travel debugging.


 He also mentioned how time travel is “not a new thing” and he was inspired by Dan Abramov, creator of Redux when he showcased Redux at JSConfEU saying how he wanted “time travel” to “reduce his action over time”.

With Redux, you get a slider that shows you all the actions over time and as you’re moving, you get to see the UI update as well. In fact, Mozilla rebuilt the debugger in order to use React and redux for its time travel feature.

Their debugger comes equipped with Redux dev tools, which shows a list of all the actions for the debugger. So, the dev tools show you the state of the app, sources, and the pause data.

Finally, Laster added how “this is just the beginning” and that “they hope to pull this off well in the future”. To use this new time travel debugging feature, you must install the Firefox Nightly browser first.

For more details on the new feature, check out the official documentation.

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Tech writer at the Packt Hub. Dreamer, book nerd, lover of scented candles, karaoke, and Gilmore Girls.


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