Edit in JSFiddle

<div> Enter alpha numeric chars with numbers in text box and click on the button</div>
<br />
<input type="text" id="abc" />
<input type="button" id="btn" value="Click Me !!!" />
<div id="num"></div>

var $ = function (id) {
    return document.getElementById(id);
};
$('btn').addEventListener('click', function () {
    $('num').innerHTML = $('abc').value.replace(/\D/g, '');
});

//To avoid shorthand just comment the above lines and uncomment the below lines.

/*
document.getElementById('btn').addEventListener('click', function() {
    document.getElementById('num').innerHTML = document.getElementById('abc').value.replace(/\D/g, '');
});
*/