That should work as you've shown. Sounds like a bug. I will look into it.

The cause is interceptors. I can't send request with that Content-Type only when I use interceptors.

Here is my code:

axios.interceptors.request.use(function (config) {
        var token = LoginStore.getJwt();
        if (token) {
            config.headers["Authorization"] = "Bearer " + token;
        }

            return config;
        }, function (error) {    
            return Promise.reject(error);
        });

Inside interceptor I can see 'Content-Type' header, but it is not sent to the server.
Do I correctly use interceptors?

Any updates on this? I have the same issue. Axios doesn't send the header I set.

This seems to be the culprit line → https://github.com/mzabriskie/axios/blob/master/lib/adapters/xhr.js#L117

Any idea why the Content-Type header is removed before the request is sent?

A workaround option is to change your data to data || {} when you're making an axios request. This will make sure data is not undefined.

It looks like the logic for removing Content-Type when requestData is undefined came in this commit 9096d34. There is no indication why it was added however.

I would vote if the requestData is undefined and method is PUT, POST or PATCH and no Content-Type has been set, then default Content-Type to application/x-www-form-urlencoded. Otherwise just honor whatever has been specified.

@mzabriskie But in the code snippet provided by @alborozd, the data is set to Querystring.stringify({...}), so requestData should not be undefined, right?

@mzabriskie I think you're right. When I use request interceptor fiddler shows that data is empty. Without interceptor I can see data and header and it works fine.

So, probably the problem occurs when you work with interceptors.

No interceptor is needed to crash this thing. I've set content type header defaults axios.defaults.headers.post['Content-Type'] = 'application/x-www-form-urlencoded';, and i can't send any payload in POST body.

I've used workaround with URLSearchParams:

    var params = new URLSearchParams();
    params.append('email', email);
    return (dispatch) => {
        axios.post('/stack/' + uri, params)

But this is not supported by Safari and IE.

Edit: Okay :) Next update on workaround. Full supported workaround is send data as query string.
data: "flashcard=" + JSON.stringify(flashcard) + "&stackUri=" + stackUri. It hurts, but it works 👍

You can use a library like qs instead:

var qs = require('qs');
axios.post('/foo', qs.stringify({ 'bar': 123 });

this is not a solution. What is difference if I will use "Querystring" or "qs" ? The problem is the header ['Content-Type'] = 'application/x-www-form-urlencoded' is empty because of interceptors.

Any updates here? Because i've lost 1h today on researching why my POSTs are not affecting API (til i reminded about that issue)... Or there are no plans to fix that and it's better to go somewhere else?

I have the same problem... still waiting for fix...

Please reopen @nickuraltsev as this is not fixed by your solution.

+1 for issue.