You can never understand one language until you understand at least two.
Geoffrey Willans, English author and journalist
Our new validation logic is good,
but wouldn’t it be nice if the duplicate-item error messages disappeared
once the user started fixing the problem, just like our nice HTML5 validation errors do?
Try it—spin up the site with ./src/manage.py runserver,
start a list, and if you try to submit an empty item,
you get the “Please fill out this field” pop-up,
and it disappears as soon as you enter some text.
By contrast, enter an item twice,
you get the “You’ve already got this in your list” message in red—and even if you edit your submission to something valid,
the error stays there until you submit the form (see Figure 17-1).
Figure 17-1. But I’ve fixed it!
To get that error to disappear dynamically, we’d need a teeny-tiny bit of JavaScript. Python is a delightful language to program in.
JavaScript wasn’t always that.
But many of the rough edges have been smoothed off,
and I think it’s fair to say that JavaScript is actually quite nice now.
And in the world of web development, using JavaScript is unavoidable.
So let’s dip our toes in, and see if we can’t have a bit of fun.
Note
I’m going to assume you know the basics of JavaScript syntax.
If not, the Mozilla guides on
MDN are always good quality. I’ve also heard ...
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