MDN文档阅读：Javascript modules

JavaScript modules

• Applying the module to your HTML
  • <script type="module" src="main.js"></script>

  • <script type="module">
    /* JavaScript module code here */
    </script>
    

https://javascript.info

• Modules, introduction

其他参考

StackOverflow

• https://stackoverflow.com/questions/44590393/es6-modules-undefined-onclick-function-after-import
• https://stackoverflow.com/questions/49338193/how-to-use-code-from-script-with-type-module