1.普通函数
缺点： 每次调用要重复判断
var addEvent = function( elem, type, handler ){
if ( window.addEventListener ){
return elem.addEventListener( type, handler, false );
}
if ( window.attachEvent ){
return elem.attachEvent( 'on' + type, handler );
}
};
2.避免每次重复判断
缺点：首次页面加载会进行一次判断，延缓页面首次加载数据onready
var addEvent = (function(){
if ( window.addEventListener ){
return function( elem, type, handler ){
elem.addEventListener( type, handler, false );
}
}
if ( window.attachEvent ){
return function( elem, type, handler ){
elem.attachEvent( 'on' + type, handler );
}
}
})();
3.惰性加载
var addEvent = function( elem, type, handler ){
if ( window.addEventListener ){
addEvent = function( elem, type, handler ){
elem.addEventListener( type, handler, false );
}
}else if ( window.attachEvent ){
addEvent = function( elem, type, handler ){
elem.attachEvent( 'on' + type, handler );
}
}
addEvent( elem, type, handler );
};
