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A BBC navigation bar component broke depending on the external monitor

How a BBC navigation bar component broke depending on which external monitor it was on Recently, my team and I fixed an absolutely bizarre bug that only one person in the team could reproduce. And to make it even weirder, she was only able to reproduce the issue when using her work laptop at home; it worked fine with the same laptop in the office.

While reproducing the issue, a console.log of our 'more' button's click event showed our 3rd clue: that, on Chrome and Firefox, the screenX and screenY properties were negative numbers. With some Ace Attorney Investigations-style logic, when we put together the fact that the bug didn't occur on Safari and that, on Chrome and Firefox, the screenX and screenY properties were negative numbers, we could deduce that browsers have an interoperability issue in how they represent screen coordinates in multi-monitor set ups. That gave us our final clue: the code assumes click events invoked by pointers have positive screenX and screenY coordinate numbers.

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