api.js

let config = {
    baseURL: process.env.apiRoute, //http://localhost:3000
    timeout: 8000,
    headers: {'X-Custom-Header': 'wb-app'}
};
const API = axios.create(config);
API.interceptors.request.use(exitingConfig => {
    if(sessionStorage.token){
        exitingConfig.headers.Authorization =  `Bearer ${localStorage.token.replace('"','')}`;
    }
    return exitingConfig;
})

export default API;

test.html

<script type="module">
  import API from './api.js'
  API.post('/login', obj).then(res => {
    sessionStorage.token = res.data.token; // {token: 'qweq.123.asd'}
  })
</script>