Skip to main content

JavaScript

Cuprite supports evaluate_script, evaluate_async_script and execute_script. Nodes can be passed as arguments and are returned as Capybara elements.

page.evaluate_script("1 + 1") # => 2
page.evaluate_script("arguments[0].innerText", find("h1")) # => "Title"
page.execute_script("document.body.style.background = 'red'")
page.evaluate_async_script(<<~JS, 100)
  const [delay, done] = arguments;
  setTimeout(() => done("ready"), delay);
JS

JavaScript errors​

Pass js_errors: true to re-raise JavaScript errors from the page as Ferrum::JavaScriptError in Ruby:

Capybara::Cuprite::Driver.new(app, js_errors: true)

Console​

page.driver.browser.console is Ferrum's console for the current page: console.* calls, browser log entries (failed resource loads, CSP violations, deprecations, ...) and uncaught exceptions. It's Enumerable over the last 1000 messages and is cleared at the end of every test.

visit "/"
page.driver.browser.console.last.text # => "Hello world"
page.driver.browser.console.select(&:error?) # => [#<Ferrum::Console::Message type=:error source=:network ...>]

Fail a test on browser errors:

after { expect(page.driver.browser.console.select(&:error?)).to be_empty }

Print what the page logged:

after { page.driver.browser.console.each { |message| warn(message) } }

Preloading scripts​

Use the :extensions option to load scripts into every page before any other script runs:

Capybara::Cuprite::Driver.new(
  app,
  extensions: [
    "/path/to/script.js",
    { source: "window.TESTING = true" }
  ]
)