SO - 27013645 - javaScript select option change

js, onchange

by codeSpy

HTML

<select id="selectBox">
    <option>A</option>
    <option>B</option>
</select>

<input type="text" id="messageTextBox" />

JavaScript

var selectBox = document.getElementById("selectBox");
selectBox.onchange = function(){
    var textbox = document.getElementById("messageTextBox");
    textbox.value = this.value;
};