How to overcome the fact that cookies are written late, after any output to the page has begun?

Question

HTTP Cookies

I write down UTM tags in cookies to substitute a hidden field with UTM_Term in the form. But as far as I understand, they are written too late, after the page is displayed and, as a result, UTM_Term is not substituted into the hidden form field. How can this be fixed?

Answer 1

is there an option to write cookies on the front? js. Otherwise it will be dancing. It is impossible within the session at the time of downloading the file and write and read. You can consider get parameter utm and use it