Chapter 16. Dipping Our Toes, Very Tentatively, into JavaScript

If the Good Lord had wanted us to enjoy ourselves, he wouldn’t have granted us his precious gift of relentless misery.

John Calvin (as portrayed in Calvin and the Chipmunks)

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? For that we’d need a teeny-tiny bit of JavaScript.

We are utterly spoiled by programming every day in such a joyful language as Python. JavaScript is our punishment. For a web developer though, there’s no way around it. So let’s dip our toes in, very gingerly.


I’m going to assume you know the basics of JavaScript syntax. If you haven’t read JavaScript: The Good Parts, go and get yourself a copy right away! It’s not a very long book.

Starting with an FT

Let’s add a new functional test to the ItemValidationTest class:

functional_tests/ (ch14l001)

def test_error_messages_are_cleared_on_input(self):
    # Edith starts a list and causes a validation error:
    self.get_item_input_box().send_keys('Banter too thick')
    self.wait_for_row_in_list_table('1: Banter too thick')
    self.get_item_input_box().send_keys('Banter too thick')

    self.wait_for(lambda: self.assertTrue(  
        self.browser.find_element_by_css_selector ...

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