e.keyCode返回按下键的ascii值
keydown->keypress->keyup

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>
<script>
    //执行顺序keydown->keypress->keyup
    //keyup键盘弹起时触发
    document.addEventListener('keyup',function (e) {
        console.log('keyup');
        console.log(e.keyCode);     //keyup和keydown ascii得到的值不区分大小写
    })
    //keydown按下时触发
    document.addEventListener('keydown',function () {
        console.log('keydown按下了');
    })
    //keypress按下触发 不识别功能键ctrl,fn等
    document.addEventListener('keypress',function (e) {
        console.log('keypress按下了');
        console.log(e.keyCode);     //区分大小写
        if(e.keyCode)
    })


</script>
</body>
</html>