Pure Javascript listen to input value change

Question

Is there any way I can create a constant function that listens to an input, so when that input value changes, something is triggered immediately?

I am looking for so

Answer 1

As a basic example...

HTML:

Script:

/* event listener */
document.getElementsByName("Thing")[0].addEventListener('change', doThing);

/* function */
function doThing(){
   alert('Horray! Someone wrote "' + this.value + '"!');
}

Here's a fiddle: http://jsfiddle.net/Niffler/514gg4tk/