“SyntaxError: Unexpected token < in JSON at position 0”

Question

In a React app component which handles Facebook-like content feeds, I am running into an error:

Feed.js:94 undefined \"parsererror\" \"SyntaxError: Un

Answer 1

For future googlers:

This message will be generated if the server-side function crashes.

Or if the server-side function doesn't even exist ( i.e. Typo in function name ).

So - suppose you are using a GET request... and everything looks perfect and you've triple-checked everything...

Check that GET string one more time. Mine was:

'/theRouteIWant&someVar=Some value to send'

should be

'/theRouteIWant?someVar=Some value to send'
               ^

CrAsH !       ( ... invisibly, on the server ...)

Node/Express sends back the incredibly helpful message:
Uncaught (in promise) SyntaxError: Unexpected token < in JSON at position 0