I think it also very much depends on your tooling & how easy it feels to start writing unit tests.

When I work in a Java project for example I always write unit tests even for personal stuff, because the IDE integration is great and it's really quick to create a test class, run it and see granular results. I don't feel the same way about testing JavaScript because the tooling at least for me hasn't worked quite as well (though that could very well be my own fault, it's been a while since I looked into it). The more cumbersome setting up and running the tests is, the more tempting it becomes to just use the console or manually test parts instead.