Javascript-DOM

如何点击按钮更换样式

<img id="imgid" src="img/1.jpg">

<button onclick="demo()">点击</button>

<script>

    function demo(){

        document.getElementById("imgid").src="img/2.jpg"

    }

</script>

如何使用句柄点击按钮弹出

<button id="bat">点击</button>
<script>
        document.getElementById("bat").addEventListener("click",function (){
            alert("hello")
        })
</script>

<button id="bat">点击</button>
<script>
        x=document.getElementById("bat")
        x.addEventListener("click",hello)
        x.addEventListener("click",world)
        function world(){
            alert("world")
        }
        function hello(){
            alert("hello")
        }
</script>