Не вникал во весь скрипт просто добавил две функции, посмотрите как устроено
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>Document</title>
<script src="https://code.jquery.com/jquery-3.3.1.min.js"></script>
</head>
<body>
<div class="input-group">
<span class="input-group-btn">
<button type="button" class="btn btn-default btn-number btn-minus" disabled="disabled" data-type="minus" data-field="quant[1]">
<i class="material-icons">remove</i>
</button>
</span>
<input type="text" name="quant[1]" class="form-control input-number" value="1" min="1" max="30">
<span class="input-group-btn">
<button type="button" class="btn btn-default btn-number btn-plus" data-type="plus" data-field="quant[1]">
<i class="material-icons">add</i>
</button>
</span>
</div>
<div id="res"></div>
<script>
f=(n, arr) => n+" "+arr[(n%100>4 && n%100<20)?2:[2, 0, 1, 1, 1, 2][(n%10<5)?n%10:5]];
var mass = ['комната', 'комнаты', 'комнат'];
s=(val)=>$('#res').text(f(val, mass));
//plugin bootstrap minus and plus
//http://jsfiddle.net/laelitenetwork/puJ6G/
$('.btn-number').click(function(e){
e.preventDefault();
fieldName = $(this).attr('data-field');
type = $(this).attr('data-type');
var input = $("input[name='"+fieldName+"']");
var currentVal = parseInt(input.val());
if (!isNaN(currentVal)) {
if(type == 'minus') {
if(currentVal > input.attr('min')) {
input.val(currentVal - 1).change();
}
if(parseInt(input.val()) == input.attr('min')) {
$(this).attr('disabled', true);
}
} else if(type == 'plus') {
if(currentVal < input.attr('max')) {
input.val(currentVal + 1).change();
}
if(parseInt(input.val()) == input.attr('max')) {
$(this).attr('disabled', true);
}
}
} else {
input.val(0);
}
});
$('.input-number').focusin(function(){
$(this).data('oldValue', $(this).val());
});
$('.input-number').change(function() {
minValue = parseInt($(this).attr('min'));
maxValue = parseInt($(this).attr('max'));
valueCurrent = parseInt($(this).val());
var mass = ['комната', 'комнаты', 'комнат'];
s(valueCurrent);
name = $(this).attr('name');
if(valueCurrent >= minValue) {
$(".btn-number[data-type='minus'][data-field='"+name+"']").removeAttr('disabled')
} else {
alert('Sorry, the minimum value was reached');
$(this).val($(this).data('oldValue'));
}
if(valueCurrent <= maxValue) {
$(".btn-number[data-type='plus'][data-field='"+name+"']").removeAttr('disabled')
} else {
alert('Sorry, the maximum value was reached');
$(this).val($(this).data('oldValue'));
}
});
$(".input-number").keydown(function (e) {
// Allow: backspace, delete, tab, escape, enter and .
if ($.inArray(e.keyCode, [46, 8, 9, 27, 13, 190]) !== -1 ||
// Allow: Ctrl+A
(e.keyCode == 65 && e.ctrlKey === true) ||
// Allow: home, end, left, right
(e.keyCode >= 35 && e.keyCode <= 39)) {
// let it happen, don't do anything
return;
}
// Ensure that it is a number and stop the keypress
if ((e.shiftKey || (e.keyCode < 48 || e.keyCode > 57)) && (e.keyCode < 96 || e.keyCode > 105)) {
e.preventDefault();
}
});
</script>
</body>
</html>