引入JavaScript文件的方法有以下几种：
<script>标签引入外部JavaScript文件：<script src="script.js"></script>
<script>
// JavaScript code here
</script>
defer属性延迟加载JavaScript文件：<script src="script.js" defer></script>
async属性异步加载JavaScript文件：<script src="script.js" async></script>
<script>元素的方式引入JavaScript文件：var script = document.createElement('script');
script.src = 'script.js';
document.head.appendChild(script);
