How to solve the problem that the message cannot be used when the element-plus is introduced locally?

Recently I am trying to write element-plus casually, so I did not configure the Node environment and build the vue scaffolding. It was referenced locally through the way of cdn file download. All aspects of the components can be used normally, but I am trying to write the message prompt box js The components don’t seem to work. I don’t know how to introduce the components of the prompt box. The official ones are all used in the scaffolding npm way. I don’t know how to use these js components like cdn or local? I urge everyone to answer! Grateful!
The following is a code snippet:

<script src="/static/js/vue.global.js"></script>
<script src="/static/js/index.full.js"></script>
<script src="/static/js/axios.min.js"></script>
<script src="/static/js/qs.min.js"></script>

.then(function (response) {
  console.log(response);
  if (response.data == "error") {
      ElMessage('this is a message.')
  }
})

But the browser console reports an error:

ElMessage is not defined