js event 2  浏览器兼容

            
                 // js event 键盘方向键                  function $(id){                         return document.getElementById(id);                      }                window.onload = function() {                $('content').onkeydown = function(event) {                    if(window.event) {    //ie                        var code = window.event.keyCode;                    } else {      //w3c                        var code = event.keyCode;                    }                                        switch(code) {                        case 37:                            alert('向左');                        break;                        case 38:                            alert('向上');                        break;                        case 39:                            alert('向右');                        break;                        case 40:                            alert('向下');                        break;                    }                }            }