var currElem = null; //will hold the element that is bold now

 function BoldText(elem) {
 
  if (elem != currElem) { //do thing if you're clicking on a bold link

   if (currElem) //if a link bold right now unbold it

	currElem.style.fontWeight='normal';

   currElem = elem; //assign this element as the current one

   elem.style.fontWeight='bold';  //make the element clicked bold
 
  }
  
}