SyntaxError: Unexpected end of JSON input

[cafer89]

good day everyone.

I have develop a front and back web app that consist of some chemical engineering calculations. In the designer>pipes>liquid page i send a post with two numbers to the backend, where after some calculations it returns the answer that gets rendered in the frontend.

I test on my localhost and everything went fine, nevertheless, when i uploaded all the repo to render and i use the form to do the post i get this error: SyntaxError: Unexpected end of JSON input.

I’ve been figuring out for two straight days and have no absolute clue what is causing this error. I have tried a lot of codes( CORS, json.text(), etc) and nothings seems to fix this error.

Does anyone have fixed this error? please help me.

The repo is on: GitHub - carlosfpj/equipment-designer at production

Thank you so much

[Jason-Render]

“Unexpected end of JSON input” errors generally mean that you received a blank response back. You should inspect the content of the result to determine what you’re actually receiving (prior to parsing it), and then determine why you’re receiving unexpected content.

[cafer89]

Thanks for your response Jason.

i will check what you said, nevertheless I’m quite surprised on my localhost worked, i mean, i receive the proper response back from the server without any problems.

I thought about the asyncronity , so y typed async/await acordingly and i’m still facing this error.

Do you know any tools to check the content of the server response?

Thank you!

[Jason-Render]

You could log the response before parsing it in your application, or craft the request using any http tool; Curl, HTTPie, Postman, etc.

[cafer89]

Hello Jason.

I took your advice and used Postman and ThunderClient to send requests to my backend, I fixed some routes stuff and it works perfect, the response comes as I expect (Json or text format, tested both).

Sadly, when I test the request and response in the browser with my render static-site I’m still getting the same error “SyntaxError: Unexpected end of JSON input” in this line in my React component:

const resJson = await res.json();

I was checking this community forum and found someone who had the exact same issue like me, the thread is in the following link:

Getting SyntaxError: Unexpected end of JSON input while using site deployed on Render

I have built a Full-stack MERN (React + Node.js + MongoDB) Note taking application. After ensuring both frontend and backend apps were working properly on my local machine, I decided to deploy them on Render. I first deployed the backend to Render, and when I tried to connect my local frontend app with the deployed backend app, it worked great. I could perform actions like Sign up/Log in without any issues. Then I deployed my frontend app on Render as well (here’s the web app - https://notes-a…

As he mentions, he changed some stuff on his proxy on the frontend package json, unfortunately he doesn’t specify what actually did he change. I asked gemini and google what is that proxy but i don’t understand quite well what is the purpose of that proxy in order to know if that’s where my error comes from.

I also tried to contact him on this forum but i guess it is not possible, there is no way to land messages between members, could be a future feature, perhaps. .

Jason, do you have any clue or any blog where I can read about this proxy thing and figure this out?

Thanks in advance.

Carlos.

[Jason-Render]

Update your application to print the request body to logs before parsing it.