example html:

<button class="bbButtons" title="Bold" accesskey="b" id="bbCode_Bold" >Bold</button>
<button class="bbButtons" title="Italic" accesskey="i" id="bbCode_Italic" >Italic</button>

<textarea id="textbox" cols="100" rows="12"></textarea>


javascript:

var theTextBox = $('#textbox')[0];  //make a reference for accessing it multiple times

var bbCode = { 	                
					bbCode_Bold :			{ encloseLeft : "[b]", encloseRight  : "[/b]"},
					bbCode_Italic :			{ encloseLeft : "[i]", encloseRight  : "[/i]"},
			   }; 

			   
				   
$('.bbButtons').mouseup(function(){    //add event handler to each button
	var buttonID = $(this).attr('id');	//assign the id of the button that was clicked to a variable									
	var currentValue = theTextBox.value; //assign the text that is currently in the textbox to a variable	
	theSelection = document.selection.createRange().text;  //assign the text that is currently selected in the textbox to a variable
	if(theSelection === ""){      //if they haven't selected anything
		if (((currentValue.split(bbCode[buttonID].encloseLeft).length+currentValue.split(bbCode[buttonID].encloseRight).length)  % 2) == 0){ //if the the number of "encloseLeft" bbcode's & the number of "encloseRight" bbcode's in the text box is even
			theTextBox.focus(); //make sure the cursor is in the text box
			document.selection.createRange().text = bbCode[buttonID].encloseLeft; //add a left bbcode (e.g. [b])
			return;		
		}
		else{   
			theTextBox.focus();  //make sure the cursor is in the text box
			document.selection.createRange().text = bbCode[buttonID].encloseRight; //add a right bbcode (e.g. [/b])
			return;				
		}
		
	}
	else{   //if they have selected text
		document.selection.createRange().text = bbCode[buttonID].encloseLeft + theSelection + bbCode[buttonID].encloseRight; //wrap the selection in the bbcode buttons and assign it to the "document.selection.createRange().text" which will paste it into the textbox
		return;
	}
	theTextBox.focus(); //make sure the cursor is in the text box
	theSelection = ""; //empty theSelection variable
});