function autoExpand(textarea) {
    // 重置高度以正确计算scrollHeight
    textarea.style.height = 'auto';
    // 设置新高度
    textarea.style.height = (textarea.scrollHeight) + 'px';
}

// 使用示例
const textarea = document.querySelector('textarea');
textarea.addEventListener('input', () => autoExpand(textarea));

/* 仅适用于部分现代浏览器 */
textarea {
    resize: none;
    min-height: 50px;
    max-height: 200px;
    overflow-y: hidden;
}

function debounce(func, wait) {
    let timeout;
    return function() {
        const context = this, args = arguments;
        clearTimeout(timeout);
        timeout = setTimeout(() => func.apply(context, args), wait);
    };
}

textarea.addEventListener('input', debounce(() => autoExpand(textarea), 100));