[bes]

для одной строки в хроме

<div contenteditable="true">write here</div>
<script>
document.querySelector("div").addEventListener("input", function () {
	var sel = window.getSelection(),
		range = sel.getRangeAt(0),
		pos = range.endOffset;
	
	this.innerHTML = this.innerHTML.substr(0, 10);
	
	try {
		range.setStart(range.startContainer , pos);
	} catch (e) {
		range.setStart(range.startContainer , pos - 1);
	}
	sel.removeAllRanges()
	sel.addRange(range);
});
</script>