js 重复调用的问题？

Question

这个问什么setInterval没有重复调用函数？

<script type="text/javascript">

function C(){this.test = "abc";}

var c = new C();

C.prototype.xx = function(obj){console.log(obj.test);}

c.xx(c);c.xx(c);c.xx(c);c.xx(c);c.xx(c);c.xx(c);

setInterval(c.xx(c),50);

</script>

Answer 1

setInterval(function() {     c.xx(c); },50);