Axios Interceptors End the Tedium of Attaching JWTs to Every Request
Scattering authentication logic across every API call creates a maintenance nightmare as projects grow. Centralizing token attachment in an interceptor keeps business code focused on data fetching and makes the entire request pipeline auditable in one place.
Manually adding an Authorization header to every Axios call is brittle and repetitive. A request interceptor on a shared Axios instance inspects each outgoing request, pulls the stored JWT from localStorage, and injects the Bearer token into the headers before the request leaves the browser. The result is that individual API modules like user.js or repo.js contain zero token logic — they simply declare which endpoint to hit. The interceptor also becomes the natural home for other cross-cutting concerns: unified headers, request logging, parameter transformation, loading indicators, and error handling. The chain completes when the server extracts the token from the Authorization header, strips the Bearer prefix, and verifies the JWT.
Many frontend authentication tutorials skip the interceptor step, leaving beginners to copy-paste headers into every call — a habit that scales poorly past three endpoints.
The Bearer-prefix formatting detail is a small but common source of silent auth failures that are hard to debug without inspecting raw request headers.
Using localStorage as the token source inside an interceptor assumes a single-tab, single-user model; multi-tab or multi-account scenarios would need a different synchronization strategy.