function init() {
   //assign event handlers.  I'm using anonymous functions to keep the number of similiar 
   //named functions low.
   document.getElementById("addboldbutton").onclick = function() { addTags("<b></b>"); };
   document.getElementById("additalicbutton").onclick = function() { addTags("<i></i>"); };
}

function addTags(tag) {
   document.getElementById("ta").value += tag;
}