js on change of input code example

Example 1: js html textbox on change

<!-- 
	You can use any of the following:
	onkeydown, onkeyup or onchange
 -->

<input type="text" onkeydown="keydownFunction()" 
onkeyup="keyupFunction()" onchange="changeFunction()">

Example 2: javascript input value change

function updateInput(ish){
    document.getElementById("fieldname").value = ish;
}