axios request interceptor adds additional headers

[eau-de-la-seine]

Describe the bug

axios request interceptor adds additional headers

To Reproduce

axios.interceptors.request.use(config => {
    console.log('config.headers')
    console.log(config.headers)
    return config
}, error => {
    return Promise.reject(error)
})

await axios.get(url, {
    headers: {"X-header1": 'headerValue1'}
})

Console Log result:

config.headers
{
  common: { Accept: 'application/json, text/plain, */*' },
  delete: {},
  get: {},
  head: {},
  post: { 'Content-Type': 'application/x-www-form-urlencoded' },
  put: { 'Content-Type': 'application/x-www-form-urlencoded' },
  patch: { 'Content-Type': 'application/x-www-form-urlencoded' },
  'X-header1': 'headerValue1'
}

Problem: common, delete, get, head, post, put, patch have been added to config.headers by axios

Expected behavior

Expected Console Log result:

config.headers
{
  'X-header1': 'headerValue1'
}

Environment

NodeJS Back-end project using ES6 modules and testing with Jasmine (the only testing framework that works without additional transpiler for ES6 projects)

• Axios Version ^0.27.2
• Node.js Version v14.17.0
• OS: Ubuntu 20.04.4 LTS
• Additional Library Versions: Jasmine ^4.2.1