如何在javascript中每n个字符后插入一个字符？

function chunk(str, n) {        var ret = [];        var i;        var len;        for(i = 0, len = str.length; i < len; i += n) {ret.push(str.substr(i, n))        }        return ret    };    chunk("The quick brown fox jumps over the lazy dogs.", 5).join('$');    // "The q$uick $brown$ fox $jumps$ over$ the $lazy $dogs."