条件预加载(conditional advanceloading)
1 var addHandler = document.body.addEventListener ? 2 function(target, eventType, handler) { 3 target.addEventListener(eventType, handler, false); 4 } : function(target, eventType, handler) { 5 target.attachEvent("on" + eventType, handler); 6 }; 7 8 var removeHandler = document.body.removeEventListener ? 9 function(target, eventType, handler) { 10 target.removeEventListener(eventType, handler, false); 11 } : function(target, eventType, handler) { 12 target.detachEvent("on" + eventType, handler); 13 };
预加载适用于一个函数马上要被用到,并且在整个页面的生命周期中频繁出现的场合。