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copied!<p>In my experience <code>String.fromCharCode(e.keyCode)</code> is unreliable. <code>String.fromCharCode</code> expects unicode charcodes as an argument; <code>e.keyCode</code> returns javascript keycodes. Javascript keycodes and unicode charcodes are <em>not</em> the same thing! In particular, the numberpad keys return a different <code>keycode</code> from the ordinary number keys (since they are different keys) while the same <code>keycode</code> is returned for both <code>upper</code> and <code>lowercase</code> letters (you pressed the same key in both cases), despite them having different <code>charcodes</code>. </p> <p>For example, the ordinary number key 1 generates an event with <code>keycode</code> 49 while numberpad key 1 (with <kbd>Numlock</kbd> on) generates <code>keycode</code> 97. Used with <code>String.fromCharCode</code> we get the following:</p> <pre><code>String.fromCharCode(49) returns "1" String.fromCharCode(97) returns "a" </code></pre> <p><code>String.fromCharCode</code> expects unicode charcodes, not javascript keycodes. The key <kbd>a</kbd> generates an event with a <code>keycode</code> of 65, independentant of the case of the character it would generate (there is also a modifier for if the <kbd>Shift</kbd> key is pressed, etc. in the event). The character <kbd>a</kbd> has a unicode <code>charcode</code> of 61 while the character <kbd>A</kbd> has a <code>charcode</code> of 41 (according to, for example, <a href="http://www.utf8-chartable.de/" rel="noreferrer">http://www.utf8-chartable.de/</a>). However, those are <code>hex</code> values, converting to decimal gives us a <code>charcode</code> of 65 for "A" and 97 for "a".[1] This is consistent with what we get from <code>String.fromCharCode</code> for these values.</p> <p>My own requirement was limited to processing numbers and ordinary letters (accepting or rejecting depending on the position in the string) and letting control characters (<kbd>F</kbd>-keys, <kbd>Ctrl</kbd>-something) through. Thus I can check for the control characters, if it's not a control character I check against a range and only then do I need to get the actual character. Given I'm not worried about case (I change all letters to uppercase anyway) and have already limited the range of keycodes, I only have to worry about the numberpad keys. The following suffices for that:</p> <pre><code>String.fromCharCode((96 <= key && key <= 105)? key-48 : key) </code></pre> <p>More generally, a function to reliably return the character from a <code>charcode</code> would be great (maybe as a jQuery plugin), but I don't have time to write it just now. Sorry.</p> <p>I'd also mention <code>e.which</code> (if you're using jQuery) which normalizes <code>e.keyCode</code> and <code>e.charCode</code>, so that you don't need to worry about what sort of key was pressed. The problem with combining it with <code>String.fromCharCode</code> remains.</p> <p>[1] I was confused for a while -. all the docs say that <code>String.fromCharCode</code> expects a unicode <code>charcode</code>, while in practice it seemed to work for ASCII charcodes, but that was I think due to the need to convert to decimal from hex, combined with the fact that ASCII charcodes and unicode decimal charcodes overlap for ordinary latin letters.</p>

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