Question

Have input text with value of 0 and two buttons plus and minus.
the weird stuff is when click the button, the increment is by 2 instead of 1…?
2 – 4 – 6…… what is wrong with the script?

$(function() {
   $(".PLUS").click(function(){
   var $this = $(this);
   var quantity = parseInt($this.siblings(".InputText").val()) +1;
   $(this).siblings(".InputText").val(quantity);
   });
});

Answer 1

I think the problem is that your script is being called twice.
Try this

$(function() {
            $(".PLUS").unbind("click");
            $(".PLUS").click(function(){
            var $this = $(this);
            var quantity = parseInt($this.siblings(".InputText").val()) +1;
            $(this).siblings(".InputText").val(quantity);
            });
        });

If it is not the problem, you can also try to change parseInt() for Number().