Axios POST request only working sometimes (MERN app)

问题

My axios POST request works about 70% of the time. There doesn't seem to be a pattern between which inputs work and which ones don't (length doesn't seem to matter). I've tried reading all of the stackoverflow questions with similar problems and nothing has worked.

    onSubmit() {
        const newInput = {
            input_text: this.state.value,
        }
        instance.post('http://localhost:4000/inputs/add/', newInput)
            .then(res => {
                console.log(res.data);
            })
            .catch(error => {
                if (error.response) {
                    console.log(error.response.data);
                    console.log(error.response.status);
                    console.log(error.response.headers);
                }
            });
    };

In this code snippet, "instance" is my axios instance which I've applied a timeout of 1000 on (just wanted to see if that would make a difference). I applied an axios interceptor on the request to try to understand more clearly what is going on, but behavior is identical with working and non-working requests. Meaning, "request was sent" is logged consistently meaning the request has sent, and the config logged looks similar between working and non working requests.

instance.interceptors.request.use(function (config) {
    console.log("request was sent");
    console.log(config);
    return config;
  }, function (error) {
    console.log(error);
    return Promise.reject(error);
  });

What the config looks like:

{url: "http://localhost:4000/inputs/add/", method: "post", data: {…}, headers: {…}, transformRequest: Array(1), …}
adapter: ƒ xhrAdapter(config)
data: {input_text: "l"}
headers: {common: {…}, delete: {…}, get: {…}, head: {…}, post: {…}, …}
maxContentLength: -1
method: "post"
timeout: 1000
transformRequest: [ƒ]
transformResponse: [ƒ]
url: "http://localhost:4000/inputs/add/"
validateStatus: ƒ validateStatus(status)
xsrfCookieName: "XSRF-TOKEN"
xsrfHeaderName: "X-XSRF-TOKEN"
__proto__: Object

I am fairly sure that in non-working instances, the request doesn't even reach the backend. This is because in the below code snippet of my backend route, non-working instances log nothing while working instances log both "this worked" and also "finished".

inputRoutes.route('/add').post(function(req, res) {
    req.body.input_output = processor.processText(req.body.input_text);
    let input = new Input(req.body);
    input.save()
        .then(todo => {
            res.status(200).json({'input': 'input added successfully'});
            console.log("this worked");
        })
        .catch(err => {
            res.status(400).send('adding new input failed');
            console.log("this didn't work");
        });
        console.log("finished");
});

Strangely enough, the POST request actually started working more frequently once I put the interceptor in... FYI, the request works 100% of the time on Postman. None of the error catches I've implemented seem to be hit as well and nothing is logged.

I would highly appreciate if anyone had any suggestions either for further debugging methods to try, or if anyone knows a solution to this problem. I've put debuggers/console.log statements everywhere unfruitfully and am out of ideas. Thanks!

来源：https://stackoverflow.com/questions/58326291/axios-post-request-only-working-sometimes-mern-app