"dependencies": {
  "@koa/router": "^8.0.8",
  "jsonwebtoken": "^8.5.1",
  "koa": "^2.12.0",
  "koa-bodyparser": "^4.3.0",
  "koa-ejs": "^4.3.0",
  "koa-jwt": "^4.0.0",
  "koa-static": "^5.0.0",
  "koa-views": "^6.2.2"
 }

const koa = require('koa');
const app = new koa();
const bodyParser = require('koa-bodyparser');
const router = require('@koa/router')();
const views = require('koa-views');
const static = require('koa-static');
const path = require('path');

app.use(bodyParser());
app.use(views(__dirname + '/views', {
 map: { html: 'ejs' }
}));

app.use(static(path.join(__dirname, '/static')));

router.get('/', ctx => ctx.render('index'));

app
 .use(router.routes())
 .use(router.allowedMethods());

app.listen(8080, () => {
 console.log('server is running at port 8080');
});

const { sign } = require('jsonwebtoken');
const secret = 'demo';
const jwt = require('koa-jwt')({ secret });

router.post('/login', ctx => {
 const { user } = ctx.request.body;
 if (user && user.username === 'vip') {
  let { username } = user;
  const token = sign({ username }, secret, { expiresIn: '1h' });
  ctx.body = {
   message: 'GET TOKEN SUCCESS',
   status: 200,
   token
  }
 } else {
  ctx.body = {
   message: 'GET TOKEN FAILED',
   status: 500
  }
 }
});

router.get('/info', jwt, ctx => {
 ctx.body = { message: `Welcome ${ctx.state.user.username}!`};
});

<form>
 <input type="text" name="username">
 <button id="submit">提交</button>
</form>
<button id="get">获取</button>
<script src="/UploadFiles/2021-04-02/axios.min.js">

首先添加登录的逻辑：


 document.querySelector('#submit').addEventListener('click', e => {
  e.preventDefault();
  const username = document.querySelector('input[name="username"]').value;
  axios.post('/login', { user: { username } })
   .then(response => {
    response = response.data;
    const { status, token, message } = response;
    if (status === 200) {
     localStorage.setItem('token', token);
    }
    alert(message);
   })
   .catch(error => alert(error.toString()));
 });


这里将服务端生成的token存入localStorage以便下次使用。
当在输入框中输入vip并点击提交按钮，后端返回如下格式的信息：

message: "GET TOKEN SUCCESS"

status: 200

token: "eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJ1c2VybmFtZSI6InZpcCIsImlhdCI6MTU5MDMyOTkxOSwiZXhwIjoxNTkwMzMzNTE5fQ.PsyLYmr-pDxxdtrBEvMccVtBr9-xtOAHdZKen4FP34c"

然后再添加获取逻辑：


document.querySelector('#get').addEventListener('click', e => {
  e.preventDefault();
  const instance = axios.create({ headers: { authorization: `Bearer ${localStorage.getItem('token')}` } });
  instance.get('/info')
   .then(response => {
    response = response.data;
    console.log(response)
    alert(response.message);
   })
   .catch(error => alert(error.toString()));
 });


此处用到了axios.create方法，该方法可以在请求头中添加token信息。用localStorage中获取token并拼成形如authorization: Bearer token的形式，然后再用示例发送get请求。
此时再点击获取按钮，会提示：





证明token是有效的。
此时去Application中把localStorage记录清除掉，再点击获取按钮，提示：





证明拦截成功。
完整示例可以去我的GitHub查看并下载。