Project 2:
Weather App using API

Overview

This project will help you build a Weather App using pure JavaScript and an external API. We will use the OpenWeatherMap API to fetch real-time weather data based on the user's city input.

What You'll Learn

• How to make HTTP requests using fetch()
• How to parse and handle JSON data
• How to build a CLI or console-based tool using JavaScript
• How to use environment variables to store API keys (Node.js only)

Step 1: Get API Access

Sign up at OpenWeatherMap and get your free API key.

Step 2: Understand the API Request

The API URL to get weather for a city looks like this:

https://api.openweathermap.org/data/2.5/weather?q=London&appid=YOUR_API_KEY&units=metric

Question:

What are the parameters in the API URL?

Answer: q is the city name, appid is your API key, and units=metric ensures temperature is in Celsius.

Step 3: Write JavaScript Code (Browser Console)

This version runs directly in the browser console. Replace YOUR_API_KEY with your actual key.

const city = "Delhi";
const apiKey = "YOUR_API_KEY"; // Replace with your real API key

fetch(`https://api.openweathermap.org/data/2.5/weather?q=${city}&appid=${apiKey}&units=metric`)
  .then(response => {
    if (!response.ok) {
      throw new Error("City not found");
    }
    return response.json();
  })
  .then(data => {
    console.log(`Weather in ${data.name}:`);
    console.log(`Temperature: ${data.main.temp}°C`);
    console.log(`Weather: ${data.weather[0].description}`);
    console.log(`Humidity: ${data.main.humidity}%`);
    console.log(`Wind Speed: ${data.wind.speed} m/s`);
  })
  .catch(error => {
    console.error("Error fetching weather data:", error.message);
  });

Weather in Delhi:
Temperature: 32°C
Weather: clear sky
Humidity: 28%
Wind Speed: 3.6 m/s

Code Description

• fetch() is used to send a GET request to the weather API.
• We check response.ok to handle invalid cities or errors.
• data.main.temp, data.weather[0].description etc. extract key weather metrics.
• Error handling with .catch() ensures graceful failure.

Question:

What happens if the user enters an invalid city name?

Answer: The API returns a 404 status, and our code throws an error with the message "City not found".

Step 4: Run in Node.js (with Readline)

This version lets users enter city names via command line:

// weather.js
const readline = require("readline");
const https = require("https");

const apiKey = "YOUR_API_KEY"; // Replace with your key

const rl = readline.createInterface({
  input: process.stdin,
  output: process.stdout
});

rl.question("Enter a city name: ", function(city) {
  const url = `https://api.openweathermap.org/data/2.5/weather?q=${city}&appid=${apiKey}&units=metric`;

  https.get(url, (res) => {
    let data = "";
    
    res.on("data", chunk => data += chunk);
    res.on("end", () => {
      const weather = JSON.parse(data);
      if (weather.cod !== 200) {
        console.error("Error:", weather.message);
      } else {
        console.log(`Weather in ${weather.name}:`);
        console.log(`Temperature: ${weather.main.temp}°C`);
        console.log(`Condition: ${weather.weather[0].description}`);
      }
      rl.close();
    });
  }).on("error", (e) => {
    console.error("Failed to fetch:", e.message);
    rl.close();
  });
});

Enter a city name: Paris
Weather in Paris:
Temperature: 21°C
Condition: few clouds

Best Practices

• Always validate API responses before accessing nested properties.
• Store API keys securely (e.g., in .env for real-world apps).
• Handle network errors and empty inputs gracefully.

Wrap-up

This project helped you connect JavaScript to a real-world weather API. You now know how to fetch, parse, and display data dynamically using modern JavaScript techniques.