Issue with ascii keycode in javascript

Question

I'm seeing a wierd issue in javascript, or maybe it's because javascript is new to me.

I am trying to allow some action if onkeypress, but only when alphanumeric or special character is pressed. This is my code:

if(e.keyCode>=32 && e.keyCode<=126 ){
    alert(e.keyCode);}
}

It does not alert if I press any special character key like {,]>. am I missing anything here?

Could you post your entire code? The above works fine for me: http://jsfiddle.net/LZhSW/ — Anthony Forloney, Jan 28 '13 at 13:13
yes, it does work for numerical key as well. I took the ASCII code from W3 http://www.w3schools.com/tags/ref_ascii.asp , but when i press any special character like [{]{><,.; it does not fall in =>32 and <=126 — Java Hunger, Jan 28 '13 at 13:27

score 1 · Accepted Answer · answered Jan 28 '13 at 13:18

1

The keyCode for a comma (,) is 188. Could this be why?

http://www.cambiaresearch.com/articles/15/javascript-char-codes-key-codes

answered Jan 28 '13 at 13:18

Kevin Brydon

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The key being that `keyCode` is **not** a reference into the ASCII table – Lightness Races in Orbit Jan 28 '13 at 13:26
I took referenced from W3schools url http://www.w3schools.com/tags/ref_ascii.asp and all special char comes under 32 to 126.. Am I refering wrong website to get ASCII code? – Java Hunger Jan 28 '13 at 13:29
@user2018223: You shouldn't be looking for ASCII codes at all, because you're using `keyCode`. – Lightness Races in Orbit Jan 28 '13 at 13:30
I am new in this field , please let me know how does it differ keyCode from ASCII codes? – Java Hunger Jan 28 '13 at 13:32
@user2018223: Didn't you read my answer? It contains _tons_ of links explaining this. There is also http://unixpapa.com/js/key.html. Please _read_. – Lightness Races in Orbit Jan 28 '13 at 13:35
(You also apparently did not read the documentation for `keyCode` before deciding to use it, which is a shame.) – Lightness Races in Orbit Jan 28 '13 at 13:38

score 1 · Answer 2 · edited May 23 '17 at 11:49

You have assumed that keyCode gives you an ASCII index, but that is not true. Your range criteria are incorrect due to this assumption.

MDN says:

In a keypress event, the Unicode value of the key pressed is stored in either the keyCode or charCode property, never both. If the key pressed generates a character (e.g. 'a'), charCode is set to the code of that character, respecting the letter case. (i.e. charCode takes into account whether the shift key is held down). Otherwise, the code of the pressed key is stored in keyCode.

keyCode is always set in the keydown and keyup events. In these cases, charCode is never set.

To get the code of the key regardless of whether it was stored in keyCode or charCode, query the which property.

For a list of the keyCode values associated with particular keys, run the example in Example 7: Displaying Event Object Constants and view the resulting HTML table.

Doing as instructed reveals that some of your "special" characters lie outside of the range limits you've specified.

Kevin also pointed out this useful table, but you'd be best off using a more canonical approach to keypress handling.

score 1 · Answer 3 · answered Jan 28 '13 at 13:36

1

You need to use the which property in most browsers and keyCode in IE only. You do have the correct event: only keypress will do if you're interested in the character typed rather than the physical key pressed.

Here's my favourite reference for this stuff: http://unixpapa.com/js/key.html

document.onkeypress = function(e) {
    e = e || window.event;
    var charCode = (typeof e.which == "number") ? e.which : e.keyCode;
    var charTyped = String.fromCharCode(charCode);

    alert("Character typed: " + charTyped);
};

answered Jan 28 '13 at 13:36

Tim Down

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Ah, excellent - I didn't fancy converting your previous answer. :) – Lightness Races in Orbit Jan 28 '13 at 13:38
@Non-StopTimeTravel: I seem to churn out variations on this answer on a weekly basis :) – Tim Down Jan 28 '13 at 13:42
Sounds like it's time for a pseudo-canonical self-answered FAQ post on the topic! – Lightness Races in Orbit Jan 28 '13 at 13:43

score 0 · Answer 4 · answered Jan 28 '13 at 13:49

You should use which, it should work in both Firefox and Chrome.

Try this:

document.onkeypress = function(e) {
    console.log(e.keyCode + " -- " + e.which + " -- " + e.charCode);

    if(e.which >= 32 && e.which <= 126 ){
        alert(e.which);
    }
};

Issue with ascii keycode in javascript

4 Answers4