Question

UPDATE: duplicate of Get cursor or text position in pixels for input element.

TL; DR – use the incredibly lightweight and robust textarea-caret-position Component library, which now supports <input ype="text"> as well. Demo at http://jsfiddle.net/dandv/aFPA7/

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Is there a way to know where the caret is inside an HTML text field?

<input type='text' /> 

I would like to position in pixels (and reposition) a div depending on the position of the caret.

Note: I don’t want to know the position in characters or in a <textarea>. I want to know position in pixels in an <input> element.

Answer 1

Using an invisible faux element

You can accomplish this by using an absolutely positioned invisible (using visibility not display) faux element that has all the same CSS properties as your input text box (fonts, left borders and left padding).

This very short and easy to understand JSFiddle is a starting point how this script should be working.
It works in Chrome and Firefox as is. And it seems it should be working in IE9+ as well.

Internet Explorer 8 (and down) would need some additional code to get caret position from start of text within input text box. I’ve even added a meter at the top to show a line every 10 pixels so you can see whether it measures correctly or not. Mind that lines are at 1, 11, 21,… pixel positions.

What this example does it actually takes all the text in text box up to caret position and puts it inside the faux element and then measures its width in pixels. This gets you offset from left of text box.

When it copies text to faux element it also replaces normal spaces with non-breaking ones so they actually get rendered otherwise if you’d position caret right after space you’d get wrong position:

var faux = $("#faux");
$("#test").on("keyup click focus", function(evt) {
    // get caret offset from start
    var off = this.selectionStart;

    // replace spaces with non-breaking space
    faux.text(this.value.substring(0, off).replace(/\s/g, "\u00a0"));
});​

Mind that faux’s right dimensions

• padding
• border
• margin

have been removed in order to get correct value, otherwise element would be too wide. Element’s box has to end right after the text it contains.

Caret’s position in pixels from start of input box is then easily gotten from:

faux.outerWidth();

The problem

There is one problem though. I’m not sure how to handle situation when text within text box is scrolled (when too long) and caret isn’t at the very end of text but somewhere in between… If it’s at the end then caret position is always at maximum position possible (input width less right dimensions – padding, border, margin).

I’m not sure if it’s possible to get text scroll position within text box at all? If you can then even this problem can be solved. But I’m not aware of any solution to this…

Hope this helps.