How about using direct axios API?

axios({
  method: 'post',
  url: baseUrl + 'applications/' + appName + '/dataexport/plantypes' + plan,
  headers: {}, 
  data: {
    foo: 'bar', // This is the body part
  }
});

Source: axios api

It turns out, if I set the Content-Type header to text/plain, it won't convert it to JSON or form data and will send it as I want.

axios.post('/my-url', 'my message text', {
  headers: { 'Content-Type': 'text/plain' }
});

You should not use a GET request to send JSON data in body. I suppose you should use either POST, PUT or PATCH to make this HTTP request. I suppose axios doesn't allow you to add data in the post body. You can try this, after changing your method type to POST on your server. But still you can find it out more deeper reading their docs. I have edited the code, you can find out your syntax issue also.

axios.post('http://url/api/package/questions?language=Persian', {'package-slug': 'six-dims'}, { headers: {'Content-Type': 'application/json'}})
 .then(function(result) { 
  console.log(result);
 });

You can set a "identity" transformResponse.

let res = axios.get("url",
{ transformResponse: (r) => r }); //null transform (we do not want to parse as JSON);

//res.data should now contain a plain unparsed string

Not sure if setting transformResponse to null does the same thing as the identity transform.

I'm pretty sure you must access the data property in the response object r. Also - since you are using the reddit API - make sure you are providing api_type in the request url (api_type=json for instance):

const axios = require('axios');
const url = 'https://old.reddit.com/api/login?api_type=json&user=username&passwd=password'
function axiosTest() {
    return axios.post(url).then((r) => {
        console.log(r.data)
        return r.data;
    })
}

For anyone reading this: Just to clarify, the api_type parameter in the request url is specific to the reddit API and most likely won't work any other API.

You dont need to do stringify the body, axios will do that for you.

axios.post(url,{
  date: "2018-08-18"
}, {
  headers: {
    "Content-Type": "application/json"
  }
})