How to return value from JavaScript using Selenium?

I appended the value to be returned using (in .js file):

document.body.innerHTML += '<div style="display:none;" id="some_id">' + value_to_be_returned + '</div>';

and accessed the value in java using (in .java file):

String return_value = (String) js.executeScript("return document.getElementById('some_id').innerHTML");

If the Javascript you want to execute is synchronous then the javascript return value will be assigned to the result of driver.execute_script() method — this is probably what you would expect, and follows the least surprise principle:

from selenium import webdriver

driver = webdriver.Chrome()

# make sure you have a `return` in the js code
js_url = driver.execute_script("return window.location.href")
print(js_url)

For asynchronous calls use driver.execute_async_script:

from selenium import webdriver

driver = webdriver.Chrome()

print(driver.execute_async_script('''
    fetch('http://httpbin.org/get')
         .then(resp=>resp.json())
         .then(data=>{alert(JSON.stringify(data)
         )});
'''))

For the specific case of jQuery.ajax() you can also force the call to be synchronous by passing async: false (by default it is asynchronous), for example the following code will return the http response text synchronously:

from selenium import webdriver

driver = webdriver.Chrome()

http_response = driver.execute_script("""
return $.ajax({
    url: 'http://httpbin.org/get', 
    async: false
}).responseText""")

print(http_response)

For asynchronous I used the following:

result = driver.executeAsyncScript(
  "var callback = arguments[arguments.length-1];" + 
  "$.ajax('someurl').success(function(data){ callback(data); });"
);