return a=b;与return 0;有什么区别？

<script type="text/javascript">

   function sortNum(a,b) {

     return 0;//输出结果为：80,16,50,6,100,1  

     return a=b;//输出结果为:1,100,6,50,16,80

   }

var myarr = new Array("80","16","50","6","100","1");

document.write(myarr.sort(sortNum));

</script>