Javascript Enabled input type when checkbox checked and disable when checkbox unchecked

my javascript is here:

function enable(id) {
        var i = (document.getElementById('haha').checked);

        if(i= true) {
        document.getElementById("nama_"+id).disabled= false;
        document.getElementById("ket_"+id).disabled= false;
        }else{
            document.getElementById("nama_"+id).disabled= true;
        document.getElementById("ket_"+id).disabled= true;
        }
        }

when i checked checkbox, the textbox will enabled, but when i unchecked, that textbox still enable, i want to this textbox go disabled after i unchecked. how can i fix this problem?