There are several points you need to consider.

At the root of it is the fact that the textarea you declare is not the one that is actually used - for any dijit Dojo generates new markup with its own event handlers which it inserts in the DOM document in place of your declaration. It passes your initial value to the newly defined node, and in certain circumstances connects event handlers you define to the new node, to run after (or instead of, in some cases) its own handlers. Unfortunately, it looks like that the Textarea dijit does not connect the key and mouse events, rather intercepting them for its own purposes (presumably to use in its resizing code). However form dijits, including dijit.form.Textarea do provide a generic onChange event, and if you set the intermediateChanges attribute to true, it fires for each keypress (default is false, so that onChange only fires when the Textarea loses focus).

The second major point is that for form dijits, the value should not accessed directly - even if you attach your current limitText call to the onChange event, it will not work as you want. You need to use the dijit's getValue() and setValue() methods.

So one way to get your example working is to add a new function:

function limitTextDijit(limitField, limitNum) {
	console.debug(limitField.getValue().length);
    if (limitField.getValue().length > limitNum) {
	limitField.setValue(limitField.getValue().substring(0, limitNum));
    }

and change your dijit declaration to:

This does have one possibly undesirable side effect - the onChange fires during page load when your initial value is transferred to the new node, and the initial text is truncated immediately. There are probably ways around this, if it is important, such as only connecting to onChange once the dijit is already created (I think doing it in a dojo.addOnLoad function would probably work).

Some other things to be aware of - because of the way dijit.form.Textarea is implemented the displayed value, and the actual value retrieved by getValue() (and submitted to the server if a form is submitted) are not necessarily the same - the actual value will have leading and trailing whitespace trimmed and intermediate whitespace consolidated (multiple spaces consolidated to a single space). This has a side effect that typing spaces at the end of a line does not cause the onChange to fire, nor do additional spaces after the first if added in the beginning or the middle of the line. Also a setValue call always moves the cursor to the end of the input, which could have some undesirable effects in your example, if the user thinks he is inserting somewhere in the middle.

Depending on what you want to achieve, you may find one of the TextBox implementations more appropriate.