if(obj.addEventListener){
    // その他ブラウザ用
}else{
    // IE用
}

<script type="text/javascript">
window.onload = function() {
    if(oButton1.addEventListener){
        oButton1.addEventListener("click", dispMsg1, false);
        oButton1.addEventListener("click", dispMsg2, false);
        oButton2.addEventListener("click", dispMsg3, false);
    }
}

function dispMsg1() {
    alert("dispMsg1");
}

function dispMsg2() {
    alert("dispMsg2");
}
function dispMsg3() {
    alert(oButton2.addEventListener);
}
</script>

<input type="button" id="oButton1" value="ボタン" />
<input type="button" id="oButton2" value="確認ボタン" />

<script type="text/javascript">
window.onload = function() {
    if(oButton3.addEventListener){
        oButton3.addEventListener("click",function(){dispMsg4('引数です')}, false);
    }
}

function dispMsg4(msg) {
    alert(msg);
}
</script>

<input type="button" id="oButton3" value="ボタン" />