<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>Document</title>
</head>
<body>
<textarea name="" id="" style="min-height: 100px;max-height: 200px;"></textarea>
</body>
<script>
var textarea = document.querySelector('textarea');
textarea.addEventListener('input', function(){
console.log(this);
this.style.height = 'auto'; // 先重置高度
this.style.height = this.scrollHeight + 'px'; // 设置为内容的高度
});
</script>
</html>