How to enable textbox on dropdown

function myFunction() {
  document.getElementById("myText").disabled = false;
}

Name:
 type="text" id="myText" disabled="true">
Click the button to disable the text field.

onchange="myFunction()"> 1 2 3
http://stackoverflow.com/questions/31647425/how-to-enable-text-box-on-drop-down-value-change-in-javascript