why request interceptors second param no run ? #7375

startjava · 2026-02-06T03:42:24Z

startjava
Feb 6, 2026

function request_error_interceptors_GET() {
            const instance = axios.create({
                baseURL: 'http://localhost:8080'
            });

            instance.interceptors.request.use(function (config) {
                // 在发送请求之前做些什么
                console.log("request在发送请求之前做些什么");
                let username = null;
                console.log(username.length);
                return config;
            }, function (error) {
                // 对请求错误做些什么
                console.log("no run no run no run no run no run n run request对请求错误做些什么 error=" + error);
                return Promise.reject(error);
            });

            instance.get("hasParam_HasReturn_NoException__Multiple_Parameters_GET?t=" + new Date().getTime(), {
                params: {
                    userId: inputValue.value,
                    citys: checkboxValue.value
                },
                paramsSerializer: function (params) {
                    return qs.stringify(params, {arrayFormat: "repeat"})
                }
            })
                .then(function (response) {
                    let getData = response.data;
                    console.log("then：");
                    console.log("code=" + getData.code);
                    console.log("message=" + getData.message);
                    console.log("data=" + getData.data);
                    console.log("");
                })
                .catch(function (error) {
                    console.log("catch：");
                    console.log(error);
                    console.log("");
                })
                .finally(function () {
                    console.log("finally");
                    console.log("");
                });
        }

how run into second param??

qtaghdi · 2026-03-18T07:12:24Z

qtaghdi
Mar 18, 2026

The second parameter of request interceptor only runs when a previous interceptor returns Promise.reject(), not when a runtime error occurs inside the first parameter.

Why

Axios interceptors work as a Promise chain internally.
The second parameter is a .catch() handler for the previous interceptor's rejected promise, not a try/catch for the current one.

So in your code, username.length throws a TypeError at runtime, which bypasses the chain entirely and is never caught by the second parameter.

How to actually trigger the second parameter

// interceptor 1 - intentionally rejects
instance.interceptors.request.use(
  (config) => Promise.reject(new Error("rejected from interceptor 1"))
);

// interceptor 2 - second parameter receives the rejection from interceptor 1
instance.interceptors.request.use(
  (config) => config,
  (error) => {
    console.log("now this runs!", error); // runs
    return Promise.reject(error);
  }
);

If you want to catch runtime errors inside a single interceptor, use try/catch explicitly.

instance.interceptors.request.use(
  (config) => {
    try {
      let username = null;
      console.log(username.length);
    } catch (error) {
      return Promise.reject(error);
    }
    return config;
  },
  (error) => {
    console.log("now this runs!", error); // runs
    return Promise.reject(error);
  }
);

My English isn't great, so I used Claude for the translation, there may be some awkward phrasing. Feel free to reply if anything is unclear.

0 replies

emilycarter6561-byte · 2026-03-18T10:07:45Z

emilycarter6561-byte
Mar 18, 2026

Appreciate the detailed report I will look into this

…

On Wed, Mar 18, 2026, 7:12 AM Engy Park ***@***.***> wrote: The second parameter of request interceptor only runs when a previous interceptor returns Promise.reject(), not when a runtime error occurs inside the first parameter. Why Axios interceptors work as a Promise chain internally. The second parameter is a .catch() handler for the *previous interceptor's rejected promise*, not a try/catch for the current one. So in your code, username.length throws a TypeError at runtime, which bypasses the chain entirely and is never caught by the second parameter. How to actually trigger the second parameter // interceptor 1 - intentionally rejectsinstance.interceptors.request.use( (config) => Promise.reject(new Error("rejected from interceptor 1"))); // interceptor 2 - second parameter receives the rejection from interceptor 1instance.interceptors.request.use( (config) => config, (error) => { console.log("now this runs!", error); // runs return Promise.reject(error); }); If you want to catch runtime errors inside a single interceptor, use try/catch explicitly. instance.interceptors.request.use( (config) => { try { let username = null; console.log(username.length); } catch (error) { return Promise.reject(error); } return config; }, (error) => { console.log("now this runs!", error); // runs return Promise.reject(error); }); My English isn't great, so I used Claude for the translation, there may be some awkward phrasing. Feel free to reply if anything is unclear. — Reply to this email directly, view it on GitHub <#7375 (comment)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/B7Z2X6EHNJKTVIZLW6FW5YT4RJD65AVCNFSM6AAAAACUFVX4XGVHI2DSMVQWIX3LMV43URDJONRXK43TNFXW4Q3PNVWWK3TUHMYTMMJYHA3DIMY> . You are receiving this because you are subscribed to this thread.Message ID: ***@***.***>

0 replies

jasonsaayman · 2026-06-11T18:12:16Z

jasonsaayman
Jun 11, 2026
Maintainer

The second parameter of the same request interceptor is not a catch block for the first parameter.

This:

instance.interceptors.request.use(
  function (config) {
    let username = null;
    console.log(username.length); // throws TypeError
    return config;
  },
  function (error) {
    // This does not catch errors thrown above
    console.log('request error', error);
    return Promise.reject(error);
  }
);

works like this internally:

Promise.resolve(config).then(onFulfilled, onRejected)

In JavaScript promises, the onRejected handler in the same .then(onFulfilled, onRejected) handles errors from the previous promise, not errors thrown inside onFulfilled.

So your TypeError is passed to the next rejection handler in the chain, or to your final .catch():

.catch(function (error) {
  console.log("catch：");
  console.log(error);
});

To catch that error inside the request interceptor, use try/catch:

instance.interceptors.request.use(
  function (config) {
    try {
      console.log("request before send");

      let username = null;
      console.log(username.length);

      return config;
    } catch (error) {
      console.log("caught inside request interceptor:", error);
      return Promise.reject(error);
    }
  },
  function (error) {
    console.log("request interceptor rejected:", error);
    return Promise.reject(error);
  }
);

If you want the second parameter of a request interceptor to run, the request must already be rejected before that interceptor runs. For example, one interceptor rejects, and another interceptor's error handler receives it:

instance.interceptors.request.use(function (config) {
  return Promise.reject(new Error("stop request"));
});

instance.interceptors.request.use(
  function (config) {
    return config;
  },
  function (error) {
    console.log("this can run:", error.message);
    return Promise.reject(error);
  }
);

The exact order depends on interceptor registration order, but the key point is the same: the second parameter handles a rejection coming into that interceptor. It does not catch exceptions thrown by the first parameter of the same interceptor.

For your example, the final .catch() is the expected place where username.length will be handled unless you wrap the interceptor body with try/catch.

0 replies

Navigation Menu

Repository navigation

why request interceptors second param no run ? #7375

Uh oh!

{{title}}

Uh oh!

Uh oh!

{{editor}}'s edit

{{editor}}'s edit

Uh oh!

Replies: 3 comments

Uh oh!

{{title}}

Uh oh!

Uh oh!

{{title}}

Uh oh!

Uh oh!

{{title}}

Uh oh!

Select a reply

Uh oh!

why request interceptors second param no run ? #7375

Uh oh!

Uh oh!

startjava Feb 6, 2026

Replies: 3 comments

Uh oh!

qtaghdi Mar 18, 2026

Why

How to actually trigger the second parameter

Uh oh!

emilycarter6561-byte Mar 18, 2026

Uh oh!

jasonsaayman Jun 11, 2026 Maintainer

startjava
Feb 6, 2026

qtaghdi
Mar 18, 2026

emilycarter6561-byte
Mar 18, 2026

jasonsaayman
Jun 11, 2026
Maintainer