What I learned debugging a Mailchimp popup on a Vanilla JS SPA for 3 days

I spent 3 days thinking my exit intent popup wasn't working. Checked the snippet. Moved it from body to head. Tested on Firefox. Ran console commands. Everything looked right.
Turns out Mailchimp cookies your browser after the first impression and won't show it again for 30 days. Every test I ran was on a browser that had already seen it.
The fix: test on a completely fresh browser with no history. Always.
Three days of debugging. One line of understanding.
That's software.
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