Some chords do not work with onkeydown (JavaScript)

Question

Some keyboards “chords” (simultaneous keystrokes) will not be correctly registered in the browser (tested by Chrome and Firefox). For example, using the code below, try the following:

1) press the "e" key (it will record "key 69")

2) while holding "e", press "]" (it will record "key 221")

3) while still holding “e” and “]”, press “i” (this will not work!)

4) however, if you go down to “i” and press “o” instead, it will successfully register “key 79”.

document.onkeydown = function(event){ var key = event.keyCode; console.log("key", key); }; 

Can someone explain what is going on here and if there is some workaround? For context, I am developing a QWERTY based music application, and I would like to play all my chords.

I know that keyCode out of date, maybe this behavior is one of the reasons?

What is the correct approach to this problem?

Demo here: https://jsfiddle.net/nt0ad2ap/

Answer 1

I am sure that 99.9% depends on the keyboard hardware itself. I tried to do e + ] + i on the keyboard connected to the laptop, but it does not work, but when I press e + ] on this keyboard and then press i on the laptop, then it works. The keyboard is usually not created to register several keys at once (except shift , ctrl and alt ), because this is usually not required. There is a special keyboard, built mainly for games, which can register several keys at once. Try googling "anti-ghosting keyboard". Here is a quora question about this topic. I have a keyboard that allows you to register 13 keys pressed at home. I will check if the code works with this keyboard after a few hours when I get home.

UPDATE:

Works great on the best keyboard. This is a hardware problem.

Answer 2

221 is keyCode for ] , and 79 is keyCode for o , so you do not get a code representing a combination of two or more keys pressed at the same time. So:

• press the "e" key (it will record "key 69") - it's OK
• while holding down the "e" button, press the "]" (it will record "key 221"). You get the code (221) for the last key pressed ]
• still holding "e" and "]", press "i" (this is not log!) - I cannot reproduce this script, I get code 73, which is the code for i
• however, if you go down to "i" and press "o", it will successfully register "key 79". - You get the code for the last click clicked o

If you need to combine keys in JavaScript, you should consider altKey , ctrlKey , shiftKey , metaKey

Here is an old example that might prove useful. Hope this helps.