var selectval = (event.KeyCode - 48); => var selectval = (event.keyCode - 48); 是KeyCode还是keyCode？

There’s nothing wrong with writing it in native language

document.addEventListener('keydown',function(event){ if(event.keyCode <=57 && event.keyCode >= 49 && event.altKey){ var selectval = (event.keyCode - 48); console.log(typeof(event.keyCode)); console.log(typeof(selectval)); console.log(selectval); } },false);

Use event.ctrlKey, event.shiftKey, event.altKey to determine whether the ctrl key, shift key and alt key are pressed

After changing several environments, this situation finally occurred. They are all the highest version of Google. I don’t know how there are several computers without undefined

The keyCode received by the new variable is undefined;
As for why I don’t understand it yet, can someone please explain the mechanism

jQuery will help you with compatibility processing, please useevent.which代替event.keyCode.

No need for jQuery:

// 获取用户单击键盘的“键值” var keyCode = event.keyCode ? event.keyCode : event.which ? event.which : event.charCode;