Cannot set headers after they are sent to the client? - node.js

Question

Here I'm trying to GET data from server, But when I try to open the browser and get the data nothing appear, Its give me the same URL in the browser.
UnhandledPromiseRejectionWarning: Error [ERR_HTTP_HEADERS_SENT]:
// Application Dependencies
require('dotenv').config();
const express = require('express');
const cors = require('cors');
const superAgent = require('superagent');
// Application Setup
const PORT = process.env.PORT || 3000;
const app = express();
app.use(cors());
//KEYS
const WEATHER_API_KEY = process.env.WEATHER_API_KEY;
const GEOCODE_API_KEY = process.env.GEOCODE_API_KEY;
const PARK_KEY = process.env.PARK_KEY;
//Route Definitions
app.get('/location', locationHandler);
app.get('/weather', weatherHandler);
app.get('/parks', parksHandler);
app.get('*', errorHandler);
//Location Handler
async function locationHandler(req, res) {
try {
console.log(req.query);
let getCity = req.query.city;
let url = `https://us1.locationiq.com/v1/search.php?key=pk.9e079e96352c63d18cf387532fa6b9ad&q=seattle&format=json`;
const locationData = await superAgent.get(url);
const apiData = JSON.parse(locationData.text);
console.log(superAgent.get(url))
res.send(superAgent.get(url));
// let aaa = new City(getCity, apiData[0].display_name, apiData[0].lat, apiData[0].lon);
// console.log(aaa);
res.status(200).send(new City(getCity, apiData[0].display_name, apiData[0].lat, apiData[0].lon));
} catch (error) {
res.status(404).send('Something went wrong in LOCATION route')
}
}

Answer 1

The response object does not batch an entire response necessarily, and might start sending it as available. HTTP requires that headers are written before anything else. Once anything else is written, it becomes impossible to send headers, such as changing the status code.
You might refactor the code to send the status first:
res.status(200)
res.send(superAgent.get(url));
res.send(new City(getCity, apiData[0].display_name, apiData[0].lat, apiData[0].lon));
} catch (error) {

Answer 2

You cannot send a response more then once.
So remove this line: res.send(superAgent.get(url));