Keystroke to ASCII Value

Question

I want to take a keystroke and get its ASCII representation. This includes when the SHIFT key is pressed, i.e.

"shift =" returns 43
"a" returns 97
"shift a" returns 65

Is there a way I can do this without writing a lot of code?

Edit:

document.onkeypress = function () {
  console.log(event.which);
}

Shouldn't it be `function (event) {...`? Otherwise, `event.which` is undefined (or am I wrong?) — flen, Mar 14 '18 at 12:00
@flen That's correct. Some browsers expose the event as a global window.event, but there are edge cases where it may be the wrong event. Support for window.event is being removed. — Aaron Cicali, Sep 12 '19 at 19:10

score 4 · Accepted Answer · edited May 23 '17 at 12:31

4

In very less code, you can do:

document.onkeypress = function () {
  console.log(event.which);
}

Check out your console after running the above code.

ps: The weight of the above code is 55 chars. ;)

Update: It should be onkeypress and not onkeydown. Thanks Timo.

edited May 23 '17 at 12:31

Community

1
1

answered Mar 30 '16 at 13:24

Praveen Kumar Purushothaman

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For my use case I specifically need ASCII codes, so this does not work. – Josh S. Mar 30 '16 at 13:27
@JoshuaSchultheiss As you expected, it returns the right keyCode. – Praveen Kumar Purushothaman Mar 30 '16 at 13:27
Oh yeah, the first one is failing. Let me find why. And how did you get `43`? – Praveen Kumar Purushothaman Mar 30 '16 at 13:28
It does not return the keyCode differentiating lowercase "a" and uppercase "A." I am making a web app that runs assembly code and to do so I need specific ASCII values. – Josh S. Mar 30 '16 at 13:29
@JoshuaSchultheiss I got 65 for `Shift + A`. – Praveen Kumar Purushothaman Mar 30 '16 at 13:29
1

Try lowercase "a" you should get 65. "shift =" should be "+" which has the ASCII value of #43 (I believe). – Josh S. Mar 30 '16 at 13:31
Let us [continue this discussion in chat](http://chat.stackoverflow.com/rooms/107748/discussion-between-joshua-schultheiss-and-praveen-kumar). – Josh S. Mar 30 '16 at 13:33
@JoshuaSchultheiss `a` gives me `65`, `Shift + =` gives me `187`. – Praveen Kumar Purushothaman Mar 30 '16 at 13:33
2

You should use `onkeypress` instead of `onkeydown` event, then it works as you wanted – Timo Mar 30 '16 at 13:35

score 0 · Answer 2 · edited May 23 '17 at 11:50

Here are the decimal encodings for the upper/lower-case "a" in 7-bit ascii (aka us-ascii).

char    decimal    hexidecimal
A       65         41  
a       97         61

http://www.asciitable.com/

Here's the thing. keyCode != ascii (necessarily). Remember lots of different keyboards, languages, etc. I can select (in software) a us-english layout on a German physical keyboard for instance. That is at an OS level.

Within the browser the form character encoding defaults to the page encoding (e.g. utf-8, iso-8859-1, etc) unless otherwise specified.

You can use the following snippet to take a look at what is in the keypress event.

document.onkeypress = function (e) {
    var charCode = (typeof e.which == "number") ? e.which : e.keyCode;
    console.log('charCode: ' + charCode + 
                ' keyIdentifier: ' + e.keyIdentifier + 
                ' which: ' + e.which + 
                ' keyCode: ' + e.keyCode + 
                ' shiftKey: ' + e.shiftKey + 
                ' ctrlKey: ' + e.ctrlKey + 
                ' altKey: ' + e.altKey + 
                ' metaKey: ' + e.metaKey);
}

The following answer explains that using keypress event is generally the only reliable way to get a character code instead of a key code. And it seems that is what you are after.

JavaScript KeyCode vs CharCode

Sure enough, using onkeypress instead of onkeydown or onkeyup gives me 65 and 97 for "A" and "a". You would need to just update your javascript to ignore events from keys you aren't interested in (ie shift, etc).

Interesting experiment would be to play with page encoding and characters outside the 7-bit ascii range and see how well this method works for getting the actual character encodings.

Keystroke to ASCII Value

2 Answers2