myElement.setAttribute("onclick", "doSomething(" +param+ " )");
myElement.onclick = function(){doSomething(param);};
<SCRIPT>var pics = Array("a","b","c");var linkElement; var linkElementChild;for (var i=0; i<pics.length; i++){linkElement = document.createElement("a");linkElementChild = document.createElement("img");linkElement.setAttribute("id", pics[i]);linkElement.setAttribute("href","javascript:void(0)");linkElement.onmousedown = function(){swap(this.getAttribute("id"));};linkElementChild.setAttribute("src",pics[i]+".jpg");linkElement.appendChild(linkElementChild);document.getElementById("smallpics").appendChild(linkElement);}//here is the action for onmousedownfunction swap(pic){ var picname = "LARGE_" + pic + ".jpg"; var big = document.getElementById("bigpic"); big.setAttribute("src",picname);}</SCRIPT>
<html><div id="smallpics"> <a href="javascript:void(0)" onmousedown="swap(a)" ><img src="a.jpg"/></a> <a href="javascript:void(0)" onmousedown="swap(b)" ><img src="b.jpg"/></a> <a href="javascript:void(0)" onmousedown="swap(c)" ><img src="c.jpg"/></a></div><img id="bigpic" src="THIS WILL CHANGE WITH EACH CLICK" /></html>