[whatwg] Standard method to get/set caret position

Greg Kilwein gkilwein at fbsdata.com
Sun Aug 29 13:59:19 PDT 2004

On Sun, 29 Aug 2004, Ian Hickson wrote:
> On Thu, 26 Aug 2004, Ted Mielczarek wrote:
> >
> > While working on a javscript tool, I needed a way to get and set the 
> > caret position in a textbox.
> Interesting. Just out of curiosity, what is it that you were doing that 
> required access to the caret position? If I may ask.

I've encountered two situations where setting or retrieving the caret
position would be useful.  The first is a situation where I'd like to
apply an input mask to a text box.  For example, I'd like the ability to
create a text box where the date delimiters (dashes or slashes) appear
automatically in a text box upon entering the field, and when the user 
types in the field, it fills into the appropriate spaces in the input box 
and sets the text selection to the next appropriate position, all while 
allowing the user to reposition the cursor within the text box with a 
keyboard or mouse without being able to edit or delete the delimiters 
(dashes or slashes).  This would be very similar to input mask features in 
certain native apps that I've used.

The second situation is an application that would like to highlight text 
in a text box or textarea for the purposes of a spell check, thesaurus, or 
search-and-replace operation.

> So I don't know. What do people think? Should we try to be backards 
> compatible with the Mozilla interface or the IE interface, or should we 
> start from scratch here, and require that people write wrappers around 
> the Moz and IE wrappers if they want compatibility? If we use something 
> already defined, what do we use? What are the use cases that matter?

I think the IE and Mozilla models are a bit complicated, and it would be
relatively easy to create a wrapper for various UAs.  Here's what I

Given a text box or textarea that I'll refer to as "tx":

tx.selectionStart: This is a read/write integer that would set or retrieve 
   the starting index of the selected text (one-based, so "1" would be 
   the first character in the string).  If nothing is selected, 0 would
   be returned.

tx.selectionEnd: This is a read/write integer that would set or retrieve
   the ending index of the selected text (one-based).

tx.position: This is a read/write integer that would set or retrieve
   the position of the caret (again, one-based).

Given these three very simple ways to access the position of the caret and
text selection, other derivatives available in IE's implementation
(inputrange.text.length, for example) would be trivial to compute
(tx.selectionEnd-tx.selectionStart).  Given that the selectionStart and
selectionEnd return 0 if nothing is selected, this would work properly in
the case of length computations.  Additionally, it would be easy to
extract the text, given functions such as substring().

This would cover everything I've wished for with cursor positioning 
within a text box or textarea and would be vastly simpler than what 
currently exists.  What do others think - is this comprehensive? Is this a 
viable solution?


More information about the whatwg mailing list