how to check select list have select any value using javascript code example

Example 1: javascript to get value of dropdown

var e = document.getElementById("elementId");
var value = e.options[e.selectedIndex].value;
var text = e.options[e.selectedIndex].text;

Example 2: select box get value

// reference to 'scripts' select list 
// used throughout the examples below
var sel = document.getElementById('scripts');

// display value property of select list (from selected option)
console.log( sel.value );