SyntaxError: Unexpected end of JSON input at JSON.parse (<anonymous>) at IncomingMessage.<anonymous>

Question

Im trying to make a weather app and I'm using a weather API to get the information but this error shows up when I'm trying to parse the JSON data: SyntaxError: Unexpected end of JSON input at JSON.parse (<anonymous>) at IncomingMessage.<anonymous> edit: I need to get the lat and lon values from an https request. I tried returning it but it will still say lon and lat is undefined.

second edit: If I input the values of lon and lat It will parse the data and send back the JSON but I need the values of lon and lat from the locaionIQ API on the https request. How do I get those values? here is the code:

const express = require('express');
const app = express();
const bodyParser = require('body-parser');
const https = require('https');
const { static, response } = require('express');
require('dotenv').config();


app.use(bodyParser.urlencoded({extended:true}));
app.use(express.static('public'))

app.listen(3000, ()=>{
  console.log("server is running on port 3000")
})

app.get('/', (req,res)=>{
  res.sendFile(__dirname+'/index.html')
})

app.post('/', (req,res)=>{
  
  let apiKeyLocationIQ = process.env.API_KEY_LOCATIONIQ;
  let apiKeyWeather = process.env.API_KEY_WEATHER;
  let cityLocationIQ = req.body.citySearch;
  let urlLocationIQ = "https://api.locationiq.com/v1/search.php?format=JSON&key="+apiKeyLocationIQ+"&q="+cityLocationIQ+"&limit=1";
  https.get(urlLocationIQ, function(response){
    response.on("data",function(data){
      let locationIQ = JSON.parse(data);
      const lat= locationIQ[0].lat;
      const lon= locationIQ[0].lon;
      const cityName = locationIQ[0].display_name;
    })
  })

  let urlWeather = 'https://api.openweathermap.org/data/2.5/onecall?&lat='+lat+'&lon='+lon+'&exclude=alerts,minutely&units=metric&appid='+apiKeyWeather+'&lang=en&cnt=7';
  https.get(urlWeather, function(response){
    response.on("data",function(data){
      let weatherData = JSON.parse(data);
      console.log(weatherData);
      
    })
  })
  
})

Answer 1

Under Node, HTTP/HTTPS request data can arrive in multiple chunks which need to be amalgamated before parsing the resultant JSON string.

Essentially JSON parsing needs to be performed in an on("end", callback) , not in an on("data", callback) , or risk incomplete JSON text.

Node documentation has an excellent working example for getting JSON data under http.get(options[, callback]) . This does not appear to be duplicated in the HTTPS section of documentation due to similarities of the HTTP and HTTPS APIs.

Answer 2

Https response data are collected in small chunks, so when its collecting data ("on"), we should append the data(string) in variable (starting with empty string [here let chunks="";])

When all the chunks of data are collected ("end"), then we should finally parse the string(API data) into JSON format.

https.get(apiLink, function (response) { 

        let chunks="";
        response.on("data", function (chunk) {
            chunks+=chunk;
        });
        response.on("end", function(){
            // console.log("API Data recieved");

            let defaultCovidData = JSON.parse(chunks);
            // code after parse string into JSON format
        });

});