JSON.parse() causes Error without any data

Question

I am writing an AWS Lambda Function.

and I would request the API without event.body for test

export const check = async (event) => {
  try{
    console.log("it does work");
    const {email, uid} = JSON.parse(event.body); // email and uid both would be undefined..
    //JSON.parse() throw some Error, so the below codes doesn't work.
    //Also, I can't see any single word from the response.
    if(!email && !uid) throw "No body data!"; // I expected throw this string but it didn't happend
    return {
      statusCode: 200,
      body: JSON.stringify({msg: "SUCCESS"})
    }
  }catch(e){
    return {
      statusCode: 500,
      body: JSON.stringify({e: e})
    }
  }
}

I could get this response.

{
  e: {}
}

I want to see

{
  e: "Some sentences about Error caused by JSON.parse() or No body data!"  
}

dumbass · Accepted Answer · 2021-01-25 14:59:10Z

2

Try this:

  }catch(e){
    return {
      statusCode: 500,
      body: JSON.stringify({e: String(e)})
    }
  }

This will leave e as-is if it is already a string or convert it to a string containing the message if it is an Error object.

edited Jan 25, 2021 at 14:59

answered Dec 3, 2019 at 8:22

dumbass

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Comments

Shihab · Accepted Answer · 2019-12-03 08:37:47Z

1

To get the error message I believe you have to do it like this:

return {
  statusCode: 500,
  body: JSON.stringify({e: e.message})
}

Or, you can use Error.prototype.toString().

return {
  statusCode: 500,
  body: JSON.stringify({e: e.toString()})
}

Remember, e.message would be undefined for your the manually throw error (throw "No body data!";). In that case, you can check if e is a string. If string the use e otherwise e.message.

edited Dec 3, 2019 at 8:37

answered Dec 3, 2019 at 8:19

Shihab

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4 Comments

kyun Over a year ago

Could I block to pass the error from JSON.parse()?

Shihab Over a year ago

You mean, you want to continue even if JSON.parse() throws an error?

kyun Over a year ago

Yes! I want to throw the error using my if-statements

Shihab Over a year ago

@zynkn, the use another (nested) try-catch to handle only the JSON.parse().

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