Read enviroment based config properties in nodejs

I am C# guy but I am writing first time node JS lambda function. I am trying to return JSON object the based on environment for example if query param ?env=prod

then expected response will be

{
    "Aws_Client_Id": "ProdAbc",
    "Aws_Secret_Key": "ProdAbc",
    "FeatureStringTest": "DefaultValue"
}

config.json

{
    "Aws_Client_Id": {
        "Deafult": "Abc",
        "Dev": "DevAbc",
        "Uat": "UatAbc",
        "Prod": "ProdAbc"
    },
    "Aws_Secret_Key": {
        "Deafult": "Abc",
        "Dev": "DevAbc",
        "Uat": "UatAbc",
        "Prod": "ProdAbc"
    },
    "FeatureStringTest": "DefaultValue"
}

my current lambda code

const fs = require("fs");

exports.handler = async (event) => {

    const jsonString = fs.readFileSync("./config.json", 'utf8');
    var config = JSON.parse(jsonString);
 
 
    const response = {
        statusCode: 200,
        body: JSON.stringify(config),
    };

    return response;
};