Use of check boxes: select all, deselect all, and select some

function ck(n){
    
        // Get all checkboxes 
        var cks = document.getElementsByName("checkbox");
        // Get the checkbox with all selected 
        var ckz=document.getElementById("checkboxs");

        var m = 0;// Calculate the number of checked products 
        if (n!=-1) {
    // Determine whether it is the select all button 
            ckz.checked=false;// Not the select all button , The button is set to false
            for (var i = 0; i < cks.length; i++) {
    
                if (cks[i].checked) {
    
                    m++;
                }
            }
            if (m==cks.length){
    
                ckz.checked=true;
            }
        }else {
    
            for (var i = 0; i < cks.length; i++) {
    
                cks[i].checked = ckz.checked;
                m++;
            }
        }
    }

n The mark is used to distinguish whether the check box is selected all , A check box