Buttons Plus & Minus

How to increment or decrement a form field using jQuery, specially useful for quantity fields.

by Zer00ne Null

HTML

<form id='myform' method='POST' action='#'>
  <input type='button' value='-' class='qtyminus' field='quantity' />
  <input type='text' name='quantity' value='0' class='qty' />
  <input type='button' value='+' class='qtyplus' field='quantity' />
</form>

CSS

#myform {
  text-align: center;
  padding: 5px;
  border: 1px dotted #ccc;
  margin: 2%;
}

.qty {
  width: 40px;
  height: 25px;
  text-align: center;
}

input.qtyplus {
  width: 25px;
  height: 25px;
}

input.qtyminus {
  width: 25px;
  height: 25px;
}

JavaScript

jQuery(document).ready(function() {
  // This button will increment the value
  $('.qtyplus').click(function(e) {
    // Stop acting like a button
    e.preventDefault();
    // Get the field name
    fieldName = $(this).attr('field');
    // Get its current value
    var currentVal = parseInt($('input[name=' + fieldName + ']').val());
    // If is not undefined
    if (!isNaN(currentVal) && currentVal < 10) {
      // Increment
      $('input[name=' + fieldName + ']').val(currentVal + 1);
    } else {
      // Otherwise put a 10 there
      $('input[name=' + fieldName + ']').val(10);
    }
  });
  // This button will decrement the value till 0
  $(".qtyminus").click(function(e) {
    // Stop acting like a button
    e.preventDefault();
    // Get the field name
    fieldName = $(this).attr('field');
    // Get its current value
    var currentVal = parseInt($('input[name=' + fieldName + ']').val());
    // If it isn't undefined or its greater than 0
    if (!isNaN(currentVal) && currentVal > 0) {
      // Decrement one
      $('input[name=' + fieldName + ']').val(currentVal - 1);
    } else {
      // Otherwise put a 0 there
      $('input[name=' + fieldName + ']').val(0);
    }
  });
});