textarea实现高度自适应

<div>
     <textarea type="text" placeholder="测试高度自适应" id="testHeight" style="height:1em"></textarea>
</div>

<script type="text/javascript">
    var testHeight = document.querySelector('#testHeight')
    testHeight.addEventListener('input', (e) => {
　　　　 testHeight.style.height = '1em';
        testHeight.style.height = e.target.scrollHeight + 'px';
    });
</script>