Do you need to take the value from the select and use it in your context? You can do that by using getElementById as you have an id associated:
let menu = document.getElementById('menu')
let tld = menu.options[menu.selectedIndex].value
window.open('searchDomain.html?...&value='+ tld)
You should make a check if nothing has been selected. My assumption is that selectedIndex will be -1 or maybe 0.