如何在onclick上选择多个类，并在选择时更改颜色

<style>
    .class1 { color: red; }
    .class2 { color: blue; }
    .class3 { color: green; }
</style>

<button onclick="changeColor()">点击选择类</button>

<script>
    function changeColor() {
        var elements = document.getElementsByClassName("class1 class2 class3");
        for (var i = 0; i < elements.length; i++) {
            elements[i].style.color = "yellow";
        }
    }
</script>