js中的forEach

<button onclick="numbers.forEach(myFunction)">
    点我
</button>
<p>
    数组元素总和：<span id="demo"></span>
</p>
<script>
    var sum = 0;
    var numbers = [65, 44, 12, 4];
    function myFunction(item) {
        sum += item;
        demo.innerHTML = sum;
    }
</script>