How to make an addition instead of a concatenation

Question

I have an input button. I created for this input an attribute called \"multiplicateur\" which has the value of 1. When the button is clicked I have a .click() t

Answer 1

For substracting

function removeFromQtt(){
             $("qty").value = parseInt($("qty").value)-1;
 }

For addition

function add(){
             $("qty").value = parseInt($("qty").value)+1;
 }