Get selected value in dropdown list using JavaScript

How do I get the selected value from a dropdown list using JavaScript?

I tried the methods below, but they all return the selected index instead of the value:

var e = document.getElementById("ddlViewBy");
function show(){
  var as = document.forms[0].ddlViewBy.value;
  var strUser = e.options[e.selectedIndex].value;
  console.log(as, strUser);
}
e.onchange=show;
show();

<form>
  <select id="ddlViewBy">
    <option value="1">test1</option>
    <option value="2" selected="selected">test2</option>
    <option value="3">test3</option>
  </select>
</form>

If you have a select element that looks like this:

<select id="ddlViewBy">
  <option value="1">test1</option>
  <option value="2" selected="selected">test2</option>
  <option value="3">test3</option>
</select>

Running this code:

var e = document.getElementById("ddlViewBy");
var strUser = e.value;

Would make strUser be 2. If what you actually want is test2, then do this:

var e = document.getElementById("ddlViewBy");
var strUser = e.options[e.selectedIndex].text;

Which would make strUser be test2