how to select value from dropdown in javascript code example

Example 1: javascript get selected option

var e = document.getElementById("selectElementID");
var value=e.selectElement.options[e.selectedIndex].value;// get selected option value
var text=e.options[e.selectedIndex].text;//get the selected option text

Example 2: 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 3: html get selected option javascript

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

<script>
    var e = document.getElementById("ddlViewBy");
	var strUser = e.value; // 2
	var strUser = e.options[e.selectedIndex].text; //test2
</script>