How to differentiate capital letters from lower ones in onkeydown event handler method

<html>
<head>
<title>Test</title>

<script type="text/javascript">

function showChar(e) {
    if (e.keyCode != 16) {
        alert(
           "keyCode: " + e.keyCode + "\n"
          + "SHIFT key pressed: " + e.shiftKey + "\n"
        );
    }
}

</script>
</head>

<body onkeydown="showChar(event);">
<p>Press any character key, with or without holding down
 the SHIFT key.<br /></p>
</body>
</html>

How can I differentiate capital A from lowercase a in onkeydown event handler method? Above algorithm fires the same keyCode value. I need to detect the capital letters when they are pressed in onkeydown.

Note: The code contains an exception for SHIFT key. Otherwise it does not allow to type capital letters. BTW, I need to use onkeydown for my trial.

It looks to me like you answered your own question. If you are detecting the SHIFT key, you can easily differentiate between capital and lowercase:

if(e.shiftKey){
   alert("You pressed a CAPITAL letter with the code " + e.keyCode);
}else{
   alert("You pressed a LOWERCASE letter with the code " + e.keyCode);
}

Or am I misunderstanding your question?

Update: Upper case ASCII codes can easily be converted to lower case ASCII codes by adding 32, so all you need to do is this:

<html>
<head>
<title>Test</title>

<script type="text/javascript">

function showChar(e){
  if(e.keyCode!=16){ // If the pressed key is anything other than SHIFT
        if(e.keyCode >= 65 && e.keyCode <= 90){ // If the key is a letter
            if(e.shiftKey){ // If the SHIFT key is down, return the ASCII code for the capital letter
                alert("ASCII Code: "+e.keyCode);
            }else{ // If the SHIFT key is not down, convert to the ASCII code for the lowecase letter
                alert("ASCII Code: "+(e.keyCode+32));
            }
        }else{
            alert("ASCII Code (non-letter): "+e.keyCode);
        }
  }
}

</script>
</head>

<body onkeydown="showChar(event);">
<p>Press any character key, with or without holding down
 the SHIFT key.<br /></p>
</body>
</html>

Update 2: Try this:

<html>
<head>
<title>Test</title>

<script type="text/javascript">

function showChar(e){
  if(e.keyCode!=16){ // If the pressed key is anything other than SHIFT
        c = String.fromCharCode(e.keyCode);
        if(e.shiftKey){ // If the SHIFT key is down, return the ASCII code for the capital letter
            alert("ASCII Code: "+e.keyCode+" Character: "+c);
        }else{ // If the SHIFT key is not down, convert to the ASCII code for the lowecase letter
            c = c.toLowerCase(c);
            alert("ASCII Code: "+c.charCodeAt(0)+" Character: "+c);
        }
  }
}

</script>
</head>

<body onkeydown="showChar(event);">
<p>Press any character key, with or without holding down
 the SHIFT key.<br /></p>
</body>
</html>

More recent and much cleaner: use event.key. No more arbitrary number codes!

node.addEventListener('keydown', function(event) {
    const key = event.key; // "a", "1", "Shift", etc.
    if (/^[a-z]$/i.test(key)) { // or if (key.length === 1 && /[a-z]/i.test(key))
        const isCapital = event.shiftKey;
    }
});

Mozilla Docs

Supported Browsers

I did quite a bit of searching on this question, as I was writing code to limit an input element (using the keyPress event) to alpha characters only. I was using "character codes between 65 and 90" and could not enter lowercase letters in the field.

I finally discovered that JavaScript is using ASCII codes for this, so I just added "and also between 97 and 122" and viola! I'm able to enter both upper and lower case letters. To wit:

function alphaOnly(e) {
    'use strict';
    if (!e) { // compensates for IE's key code reporting.
        e = window.event;
    }
    var charCode = (e.which) ? e.which : event.keyCode;
    if ((charCode >= 65 && charCode <= 90) || (charCode >= 97 && charCode <= 122)) {
        return true;
    } else {
        return false;
    }
}

来源：https://stackoverflow.com/questions/3125727/how-to-differentiate-capital-letters-from-lower-ones-in-onkeydown-event-handler

标签

javascript

onkeydown