想通过按键控制一个块移动，这段代码为何不起作用

Question

document.keydown = function(event){ var event = event || window.event; var keyCode = event.keyCode || event.which; switch(keyCode){ case 37: if(speedX == 0){ speedX = -1; speedY = 0; } break; case 38: if(speedY == 0){ speedX = 0; speedY = -1; } break; case 39: if (speedX == 0){ speedX = 1; speedY = 0; } break; case 40: if(speedY == 0){ speedX = 0; speedY = 1; } break; default: return; break; } boxMove(); }   控制台没有报错，元素获取也没有问题 但是用下面这段就可以，为什么会这样 document.addEventListener("keydown",function(event){ var event = event || window.event; var keyCode = event.keyCode || event.which; switch(keyCode){ case 37: if(speedX == 0){ speedX = -1; speedY = 0; } break; case 38: if(speedY == 0){ speedX = 0; speedY = -1; } break; case 39: if(speedX == 0){ speedX = 1; speedY = 0; } break; case 40: if(speedY == 0){ speedX = 0; speedY = 1; } break; default: return; break; } boxMove();},false);

Answer 1

不知道你这个speedX、Y是什么意思，但是上面的事件应该是document.onkeydown，不是keydown