Javascript:handle Unexpected JSON error in express js

Question

I am trying to handle Unexpetced JSON in my express js application via try and catch, so what I am trying to do is

try{
  let body = JSON.parse(req.body);
}catch(e){
   res.json({
    error:e
  })
}

But the Unexpected JSON error not thrown in the catch block.

Content-type is application/json

Here is the JSON request

{
    "userId":"eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJlbWFpbCI6InNoYW1vbjVAYWNjdWJpdHMuY29tIiwiaWQiOjExNCwiaWF0IjoxNTMxOTgyNDQ0LCJleHAiOjE1MzI1ODcyNDR9.dv1zEnLsmKXbSE4wKbSOdYX3p7v5N5nh9kbz6PA_4TE",
    "readValue":falseuyuyuyu
}

readValue is malformed

Could you please check it once more, I hope the error is actually there in `catch` block. What `res.json({ error:e })` suppose to do? — jukben, Jul 26 '18 at 09:36
The JSON is wrong though, can't have string without quotation marks (unless it's a typo) — Baruch, Jul 26 '18 at 09:42
@Baruch yes JSON is wrong that i want to catch in error block — shamon shamsudeen, Jul 26 '18 at 09:43
Possible duplicate of [Handling bad JSON.parse() in node safely](https://stackoverflow.com/questions/29797946/handling-bad-json-parse-in-node-safely) — Baruch, Jul 26 '18 at 09:45
Is it possible you're already using a body parser, and so you're attempting to parse a JS object? — Richard, Jul 26 '18 at 09:55
At least in node.js console all works fine. I mean exception trown and passed to `catch` block — Vasyl Moskalov, Jul 26 '18 at 11:43

dima golovin · Answer 1 · 2018-07-26T12:00:56.490

you are missing " in the value of 'readValue'. it should be as follow :

{
"userId":"eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJlbWFpbCI6InNoYW1vbjVAYWNjdWJpdHMuY29tIiwiaWQiOjExNCwiaWF0IjoxNTMxOTgyNDQ0LCJleHAiOjE1MzI1ODcyNDR9.dv1zEnLsmKXbSE4wKbSOdYX3p7v5N5nh9kbz6PA_4TE",
"readValue":"falseuyuyuyu"
}

Edit: sorry didnt understand the question

Express has its own error handling middleware. in case of error, Express catches the error (in sync code) and handles it, That's why you cant get the error message. What you need to do is to write your own middleware that handles errors in your format. Please go to : https://expressjs.com/en/guide/error-handling.html and check Writing error handlers section.

Topic starter know that the json is incorrect. The question is "why exception do not thrown?" — Vasyl Moskalov, Jul 26 '18 at 11:41

Javascript:handle Unexpected JSON error in express js

1 Answers1