关于数组排序的问题

<script type="text/javascript">
 function sortNum(a,b) {
 return a - b;
}
var myarr = new Array("80","16","50","6","100","1");
 document.write(myarr + "<br>");
 document.write(myarr.sort(sortNum));   // 这里调用sortNum()，为什么不需要传参数进去？
</script>