What causes proxy to stop working in a React app?

Question

My React/FastAPI application had proxy

proxy": "http://localhost:8000

in my package.json working fine but now the proxy doesn't work and I get back

Internal Server Error (500) Unexpected token P in JSON at position 0

I tried

http://127.0.0.1:8000

for proxy and the same problem.

I checked the FastAPI backend and everything works fine. If I put the whole path inside fetch, then there is no problem.

I know if the error said Unexpected token < then that means I got back some HTML instead of JSON but I don't know what the P means in this error.

I upgraded Node. Could that be the cause of the error? What exactly breaks proxy?

Thank you

Answer 1

It appears that Node v17.x.x was causing problems with my proxy. I downgraded to v16.14.2 (which was approximately the version that I had before the update/upgrade) and the problems are gone. I am going to see how it goes but something about node v17 is causing problems with proxy.