Limit Number of Checkboxes Checked

Question

I have a form with several checkboxes. I have three categories of checkboxes in the form. I need to limit to a max of three checkboxes per category.

I used

Answer 1

This is a newbie code with javascript. It's like working...hardly... I call this function on each input. But there is surely a way to call this function one time. It's working but uncheking a random checkbox from thoses who call it.

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  function just2cat()
        {
            var allInp = document.getElementsByTagName('input');
            const MAX_CHECK_ = 2; /*How many checkbox could be checked*/
            var nbChk =0;
            for(var i= 0; i MAX_CHECK_) 
                    {
                        alert("At most 2 categories can be chosen");
                        allInp[i].checked=false; /* try to Unchek the current checkbox :'(  */
                    }

                }
            }
        }