问题：我的var t=setInterval(function(){svg.attr("transform","rotate(10)");},1000);为什么只能执行一次，而不能一直旋转
<!DOCTYPE html>
<head>
<meta charset="UTF-8">
<title>风扇</title>
<script type="text/javascript" src="d3.js"/>
<script src="d3-timer.v1.min.js"></script>
<style type="text/css"></style>
</head>
<body bgcolor="white"><br>
<script>
d3.xml("fengshan4.svg", function(error, documentFragment) {
if (error) {
console.log(error);
return;
}
var svgNode = documentFragment.getElementsByTagName("svg")[0];
//d3's selection.node() returns the DOM node, so we
//can use plain Javascript to append content
//use plain Javascript to extract the node
var main_chart_svg = d3.select("body").append("div");
main_chart_svg.select("svg").remove();
main_chart_svg.node().appendChild(svgNode);
var svg = main_chart_svg.select("svg");
//它返回一个现成的DOM树，可以将其插入到主文档的DOM中，无论是否需要它
svg.call(zoom);
var t=setInterval(function(){svg.attr("transform","rotate(10)");},1000);
});
</script>
</body>
