Show or Hide Div On Key Up

HTML

<label>Type whatever</label>
<form id='inptOne'>
<input id='inptOne' type="text" name="amount" onkeyup="myFunction()" />
</form>
<div id="yeah" style="display:none">
    <input type="submit" />
</div>

JavaScript

window.myFunction = function() {
    //alert('it ran!');
    var hasValue = document.getElementById('inptOne').value;
    if (!!hasValue) {
        document.getElementById('yeah').style.display = 'inline';
    } else {
	    document.getElementById('yeah').style.display = 'none';
	};
};