function inputCheck()
        {
            var check = document.forms["drinkList"]["quant1"].value
            if (isNaN(check))
            {
                window.alert("Input numbers only");
                return false;
            }
        }

<input onchange="inputCheck(this)">

function inputCheck(elem){
    var check = elem.value;
    if (isNaN(check))
    {
        window.alert("Input numbers only");
        return false;
    }
}

var names = ['quant2', 'quant3', 'quant4', 'quant5', 'whip', 'cream', 'sugar', 'chocolate', 'caramel2'];
document.body.addEventListener('keyup', function (e) {
  // skip event if it was NOT triggered on a matching element
  if (names.indexOf(e.target.name) === -1) { return; }

  // code to process event...
});

$("#drinkList .nonNumberTextbox").each(function(index, node) {
    if (isNaN(node.value)) {
        window.alert("Input numbers only");
        return false;
    }
});

if (check.trim() === '' || isNaN(+check)) {

if (isNaN(parseInt(check, 10))) { // if only integers are allowed
}

if (isNaN(parseFloat(check))) { // if integers and decimals are allowed
}

if(!/^d+$/.test(check)) { // if the number needs to be an integer
}

if(!/^d+(?:.d*)?$/.test(check)) { // if the number can be an integer or a decimal
}

var textboxes = ['quant2', 'quant3', 'quant4', 'quant5', 'whip', 'cream', 'sugar', 'chocolate', 'caramel2'];

for (var i = 0; i < textboxes.length; i++ ){
  var check = document.forms["drinkList"][textboxes[i]].value;
  if (isNaN(check)){
    window.alert("Input numbers only");
    break;
  }
}