ivt22,
непонятно о чём вы ... вариант для плюс/минус
<!DOCTYPE HTML>
<html>
<head>
<title>Untitled</title>
<meta charset="utf-8">
<style type="text/css">
.minus, .plus{
cursor: pointer;
}
</style>
</head>
<body>
<table id="result_table" border="1">
<thead>
<tr>
<th>Номер по каталогу</th>
<th>Наименование</th>
<th>Цена</th>
<th>Количесвто</th>
</tr>
</thead>
<tbody>
<tr>
<td>312304-П</td>
<td>Шайба</td>
<td>2000 р.</td>
<td>
<div class="number">
<span class="minus" >-</span>
<input type="text" value="1" id="inp4">
<span class="plus" >+</span>
</div>
</td>
</tr>
<tr>
<td>236-10020-А5</td>
<td>Блок цилиндров</td>
<td>345 р.</td>
<td>
<div class="number">
<span class="minus" >-</span>
<input type="text" value="3" id="inp5">
<span class="plus" >+</span>
</div>
</td>
</tr>
<tr>
<td>236-1004355181</td>
<td>Шайба</td>
<td>1435 р.</td>
<td>
<div class="number">
<span class="minus" >-</span>
<input type="text" value="6" id="inp6">
<span class="plus" >+</span>
</div>
</td>
</tr>
</tbody>
</table>
<script>
window.addEventListener("DOMContentLoaded", function() {
var d = document.querySelectorAll(".number");
[].forEach.call(d , function(el) {
el.addEventListener("click", function(c) {
c.preventDefault();
var i = el.querySelector("input");
c = c.target;
if (c.classList.contains("minus")) i.value--;
else if (c.classList.contains("plus")) i.value++;
else return;
0 > +i.value && (i.value = 0);
/* ограничение текущим значеним */
//+i.defaultValue < +i.value && (i.value = i.defaultValue);
},false)
});
});
</script>
</body>
</html>