jquery计算鼠标和指定元素之间距离的方法

(function() {  var mX, mY, distance,    $distance = $('#distance span'),    $element = $('#element');  function calculateDistance(elem, mouseX, mouseY) {    return Math.floor(Math.sqrt(Math.pow(mouseX - (elem.offset().left+(elem.width()/2)), 2) + Math.pow(mouseY - (elem.offset().top+(elem.height()/2)), 2)));  }  $(document).mousemove(function(e) {     mX = e.pageX;    mY = e.pageY;    distance = calculateDistance($element, mX, mY);    $distance.text(distance);       });})();