selenium button click not triggering inline javascript event handler

Question

My HTML looks like below

<div class="container">
    <div class="jumbotron">
        <h1 id="survey-title" class="display-5 text-capitalize">Your favourite candidate</h1>
        <hr class="my-4">

        <div class="card-body">
            <h5 id="question-title" class="card-title">What is your name?</h5>

            <form id="question_form" action="/survey/takesurvey/1/2" method="post" class="form">
                <input type="hidden" name="csrfmiddlewaretoken" value="ELBWYGZRxRuI7CoZ2xkmgCJ3f9JweFMM4Ew1pQbgSE3BLb38VStPJEbHvsyiBEFg">
                <div class="form-group"><input type="text" name="response" value="asdfasdfas" maxlength="400" class="form-control" title="" id="id_response"></div>
            </form>
        </div>

        <a id="btn-previous" href="javascript:history.back()" class="btn btn-primary ">Previous</a>
        <a id="btn-next" href="/survey/takesurvey/finish/1" class="btn btn-primary">Next</a>
    </div>
</div>

Notice the href on previous button

<a id="btn-previous" href="javascript:history.back()" class="btn btn-primary ">Previous</a>

Clicking next will submit form and go to "next" page, again clicking "previous" should come back and preserve the input value in previous page. I am using following code to test this behavior, The following code is working only when I put sleep(1) line in between finding the element and clicking. Else the page is not going back (url not changing)

• Why just waiting for url change before clicking the button not working
• I suspect it has to do with javascript event handler (which is inline in html) not being loaded.
• I is there any way to check if page is ready for the click event

cur_url = self.browser.current_url
self.browser.find_element_by_id('btn-next').click()

wait(lambda: self.assertNotEqual(self.browser.current_url, cur_url))
btn_previous = self.browser.find_element_by_id('btn-previous')

## This code is not working without the sleep below. Which I suspect 
## has to do with javascript event handler (which is inline in html) not being loaded.
## Is there better way to check that the button is ready to be clicked
sleep(1)

btn_previous.click()

Answer 1

You can use WebDriverWait with element_to_be_clickable condition. Check here also.

from selenium.webdriver.common.by import By
from selenium.webdriver.support.ui import WebDriverWait
from selenium.webdriver.support import expected_conditions as EC

WebDriverWait(self.browser, 5).until(EC.element_to_be_clickable((By.ID, "btn-previous"))).click()

You can try wait for JavaScript:

WebDriverWait(self.browser, 20).until(lambda d: d.execute_script(
        'return (document.readyState == "complete" || document.readyState == "interactive")'))

# or without interactive 
WebDriverWait(self.browser, 20).until(lambda d: d.execute_script(
        'return document.readyState == "complete"'))

Answer 2

This is not the desired solution but a workaround the worked for me for now.

My functions for wait

from time import sleep
from functools import wraps
from selenium.common.exceptions import NoSuchElementException

def wrap_in_wait(func, retires=5):
    @wraps(func)
    def wrapper(*args, **kwargs):
        return wait(func, *args, retires=retires, **kwargs)
    return wrapper

def wait(func, *args, retires=10, exceptions=[AssertionError, NoSuchElementException], **kwargs):
    for i in range(retires):
        try:
            return func(*args, **kwargs)
        except Exception as e:
            print('retry', i)
            if type(e) not in exceptions:
                raise e

            if i == retires-1:
                raise e

            sleep(0.5 + i*.2)

Test function with Work around solution

def test_question_form_is_loaded_with_existing_answer(self):
        '''Test question form pre-loads'''
        self.browser.get(self.live_server_url + self.url)
        inp = self.browser.find_element_by_css_selector("input#id_response")
        inp.send_keys("This is my answer")

        self.browser.find_element_by_id('btn-next').click()

        @wrap_in_wait
        def click_previous_button():
            btn_previous = self.browser.find_element_by_id('btn-previous')
            btn_previous.click()
            inp = self.browser.find_element_by_css_selector("input#id_response")
            self.assertEqual(inp.get_attribute('value'), "This is my answer")

        click_previous_button()

This solution retries click_previous_button for 10 times if it raises AssertionError or NoSuchElementException exception. It is working on 2nd try.

But I am still not sure why javascript event is not triggered even when the button is clickable and if there is direct way to test when javascript is ready