Axios interceptors with Node.js http and browser XHR/fetch adapters: binary data transformation consistency?

Binary Data Representation in Axios Interceptors

Axios interceptors do not provide a uniform representation of binary data across different adapters. The type of the payload received in an interceptor depends entirely on the environment and the adapter being used.

Request Interceptors

In a request interceptor, config.data remains the original type passed to the Axios request method. Axios does not perform automatic normalization of binary types before they hit the interceptor:

• Node.js: If you pass a Buffer, the interceptor sees a Buffer.
• Browser: If you pass an ArrayBuffer or Blob, the interceptor sees that specific type.

Response Interceptors

Response interceptors receive response.data as delivered by the underlying adapter. Because the Node.js http adapter and browser XHR/Fetch adapters utilize different native binary handles, the types diverge:

Environment	Adapter	Typical Binary Type in Interceptor
Node.js	http	Buffer
Browser	XHR / Fetch	ArrayBuffer (if responseType: 'arraybuffer')
Browser	XHR / Fetch	Blob (if responseType: 'blob')

Enforcing Consistency

There is no built-in Axios configuration option to force a single binary type across all adapters. To achieve consistency, you must implement a manual transformation. The most reliable common denominator is the Uint8Array, as it is supported in both modern browsers and Node.js.

To normalize response data, use a response interceptor or the transformResponse array:

axios.interceptors.response.use((response) => {
  if (response.data instanceof Buffer) {
    // Convert Node.js Buffer to Uint8Array
    response.data = new Uint8Array(response.data);
  } else if (response.data instanceof ArrayBuffer) {
    // Convert Browser ArrayBuffer to Uint8Array
    response.data = new Uint8Array(response.data);
  }
  return response;
});

Verification Steps

To verify the types in your specific version of Axios (assumed 1.x), use the following checks within your interceptors:

• Node.js: Log Buffer.isBuffer(response.data).
• Browser: Log response.data.constructor.name to distinguish between ArrayBuffer and Blob.

Diagnostic Detail Required: If you are using a custom adapter or a specific polyfill for Buffer in the browser, please specify, as this may lead to Buffer types appearing in browser interceptors.