jQuery查找最接近的类并增加价值

Question

I have buttons to increase/decrease quantity in a cart

<div class="product-quantity">
  <button class="qtyminus">-</button>
  <input type="text" name="quantity" value="1" class="qty form-control">
  <button class="qtyplus">+</button>
</div>

my javascript unfortunately doesn't work can't figure out why.

$('.qtyplus').on('click', function(e) {
    e.preventDefault();
    var num = Number($(this).closest('.qty').val());
    $(this).closest('.qty').val(++num);
});

Answer 1

jQuery closest searches ancestors, but in this case, you're looking for the sibling element. Try siblings instead of closest

By the way, modern browsers have built-in debugging tools. It's easy to set a breakpoint and step through you code to see what's happening, and to use the console window to test things.

Answer 2

You should use siblings() instead of closest() as closest() searches for ancestors while siblings() searches for siblings of an element.

 <script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script> <div class="product-quantity"> <button class="qtyminus">-</button> <input type="text" name="quantity" value="1" class="qty form-control"> <button class="qtyplus">+</button> </div> <script> $('.qtyplus').on('click', function(e) { e.preventDefault(); var num = Number($(this).siblings('.qty').val()); $(this).siblings('.qty').val(++num); }); $('.qtyminus').on('click', function(e) { e.preventDefault(); var num = Number($(this).siblings('.qty').val()); $(this).siblings('.qty').val(--num); }); </script> 

Answer 3

Your issue is because closest() looks up the DOM, yet .qty is a sibling to the clicked buttons, so you need to use siblings() instead.

Also note that you can use a single event handler for both buttons if you put a common class on them and provide the value to add in a data attribute. You can also negate the need to repeatedly select the same element by providing a function to val() which returns the new value based on its current one. Try this:

 $('.amendqty').on('click', function(e) { e.preventDefault(); var inc = $(this).data('inc'); $(this).siblings('.qty').val(function(i, v) { return parseInt(v, 10) + inc; }); }); 

 <script src="https://ajax.googleapis.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script> <div class="product-quantity"> <button class="amendqty" data-inc="-1">-</button> <input type="text" name="quantity" value="1" class="qty form-control"> <button class="amendqty" data-inc="1">+</button> </div>