This is the same report as #1386, it shouldn't have been closed because only a workaround was provided and this needs at least a documentation update because it's highly unexpected.

Describe the bug

While writing a request interceptor and accessing config.data you receive a JSON object, but if you access the error.config.data it's a string (JSON stringified of the original object). This is misleading if you want to retry the request (i.e axios.request(error.config)) and the request interceptor is expecting an object.

To Reproduce

axios.interceptors.request.use(config => {
  assert(typeof config.data === 'object');
  
  return config;
});

axios.interceptors.response.use(() => (),
  (error) => {
    // this fails, error.config.data is a string
    assert(typeof error.config.data === 'object');
  });
  
axios.post('https://non-existent-url-03203o1023o103o/data', {hello: 'world'});

Expected behavior

The object should be preserved for consistency as both parameters are called "config", or at least the documentation should point out this difference.

Environment

• Axios Version 0.21.1
• Node.js Version 14.17.0

Additional context/Screenshots

N/A