javascript - set cursor to specific position on specific line in a textarea -

i trying duplicate "autocorrect" functionality seen in programs microsoft office's outlook.

for starters, anytime user types "a " (the letter , space) @ beginning of line want change text "*agent ["

i have written below works fine if typing along in textarea top bottom. but if type anywhere else in textarea text changed cursor moves end of textarea.

i want cursor placed @ end of changed text.

i have line number changed in variable currentlinenumber , know cursor needs after 8th character in line unsure of how tell go there

ideally id

function setcursor(row, position) {  //.... code set cursor  } 

what can accomplish this? im open javascript or jquery solution (although find jquery little difficult read , understand)

if there's better way achieve need overall, i'm open too.

here's jsfiddle if don't understand issue

i've updated fiddle see: http://jsfiddle.net/eghpf/2/

i've added var currentposition used in method

function setselectionrange(input, selectionstart, selectionend) {   if (input.setselectionrange) {     input.focus();     input.setselectionrange(selectionstart, selectionend);   }   else if (input.createtextrange) {     var range = input.createtextrange();     range.collapse(true);     range.moveend('character', selectionend);     range.movestart('character', selectionstart);     range.select();   } } 

which comes jquery set cursor position in text area

what happens (is reason why cursor on last position); when call $('#systemnotesbuilder').val(arrayoflines.join("\n")); entire value gets overwritten new value placing cursor after new value. call set cursor (and should) after call.