Somebody asked me how to set a hidden field value to a cookie value in Formulate using the plain JavaScript template. There are two straightforward ways of doing this. For both, I recommend creating a new field category and setting the field to have that category.

For the first approach, you can set the field value to the cookie value using JavaScript. This page has a function to get a cookie value: https://www.w3schools.com/js/js_cookies.asp

You can then set the value of your field to that cookie value:

document.querySelector("[data-category='Something']").value = getCookie("Something");

Change out the name of your field category and cookie.

This talks a bit about how it can be done server side: https://our.umbraco.com/packages/backoffice-extensions/formulate/formulate-questions/87639-no-code-generate-by-hidden-field

And if you are still using the AngularJS template: https://our.umbraco.com/packages/backoffice-extensions/formulate/formulate-questions/93777-formulate-set-hidden-field