How can I parse event parametet in lambda? - node.js

Question

I am using Node.js 8.10 in lambda proxy integration.
My goal is very simple.
send json data to lambda function
query rds with json data and retrive data from rds
return response with json data in lambda from rds data.
but I faced issue in step 1. I tried to figure out and I asked aws support center. it was not helpful. please help me.
my test json data are :
{
"key1": "value1",
"key2": "value2",
"key3": "value3"
}
my code is very simple but have a problem :
exports.handler = async (event) => {
var body = JSON.parse(event)//<--this is a problem
let responseBody = {
message: "hello",
key1: body.key1
};
const response = {
statusCode: 200,
headers : {"Access-Control-Allow-Origin" : "*"},
body: JSON.stringify(responseBody)
};
return response;
};
I got this error in second line.
{"errorMessage":"Unexpected token o in JSON at position 1","errorType":"SyntaxError","stackTrace":["JSON.parse (<anonymous>)","exports.handler (/var/task/index.js:2:21)"]}
So I changed second line code like this.
var body = JSON.parse(JSON.stringify(event))
and then I got response well. I thought that's working well.
{
"statusCode": 200,
"headers": {
"Access-Control-Allow-Origin": "*"
},
"body": "{\"message\":\"hello\",\"key1\":\"value1\"}"
}
but I sent same json data with postman for real. but I got only this.
{
"message": "hello"
}
there isn't "key1". so I added console.log and then I checked log in cloudwatch.
{ message: 'hello', key1: undefined }
I can see aws editor log is well but when I send data with postman. lambda couldn't parse my json data. it means lambda couldn't parse event parameter.
my questions are :
1. when I tried to parse like this
var body = JSON.parse(event)"
why does lambda editor issue error? Is there something wrong? this is super simple and very common code.
How can I parse my json data and return correct value not undefined. I expected this response
{ message: 'hello', key1: 'value1' }
I have been trying to solve this for 3days. but I really have no idea. please help me out.

Answer 1

The body coming from API Gateway is a stringified JSON, so you need to parse it and then access the attribute you want.
'use strict';
exports.handler = async (event) => {
let responseBody = {
message: "hello",
key1: JSON.parse(event.body).key1
};
const response = {
statusCode: 200,
headers: { "Access-Control-Allow-Origin": "*" },
body: JSON.stringify(responseBody)
};
return response;
};
This will do it.

Answer 2

you need to pass the parameters in postman as JSON.
in the body tab choose the 'raw' option and then from the combo box select 'JSON' type:
then just type :
{
"key1": "value1",
"key2": "value2",
"key3": "value3"
}
and in your lambda function access to it like this:
JSON.parse(event.body).key1