Javascript comma!

The comma operator evaluates both of its operands (from left to right) and returns the value of the second operand.

as seen in Google recaptcha's js:

if (RecaptchaOptions.theme == "custom") {
    if (RecaptchaOptions.custom_theme_widget) Recaptcha.widget = Recaptcha.$(RecaptchaOptions.custom_theme_widget);
    Recaptcha.challenge_callback()
} else 
    document.write('<div id="recaptcha_widget_div" style="display:none"></div>'),
    document.write('<script>Recaptcha.widget = Recaptcha.$("recaptcha_widget_div"); Recaptcha.challenge_callback();<\/script>');