How to return a value when using execute_script in capybara?

I have a really simple line in a test that calls execute script like this:

puts page.execute_script("return somefunction();").to_i.inspect

And in javascript I have a function like this:

function somefunction(){
    console.log("test");
    return 999;
}

The 'test' from the console log is getting logged out so it is running however...

Looking at the logs when running the test, the execute_script returns 0 not 999, so in rspec I can't get at the return value from the function, how do I make page.execute_script return that value from that function?

The Poltergeist driver is designed to return nil for execute_script:

def execute_script(script)
  browser.execute(script)
  nil
end

Poltergeist will only return a value if you use the evaluate_script:

def evaluate_script(script)
  browser.evaluate(script)
end

Capybara has corresponding methods for each - ie Session#execute_script and Session#evaluate_script. Your code should work if you switch to using evaluate_script (and as @AndreyBotalov points out, you also need to remove the return):

puts page.evaluate_script("somefunction();").to_i.inspect