Using the
Fetch API
to Get and Post Data

Introduction to Fetch API

The fetch() API in JavaScript is a modern, promise-based way to make HTTP requests to servers. It works in all modern browsers and replaces the older XMLHttpRequest API with a cleaner and more powerful interface.

Why Use Fetch?

• It returns Promises — making asynchronous programming more elegant
• Supports JSON and other content types out-of-the-box
• Allows better control over requests and responses

Example 1: GET Request Using Fetch

Let's fetch a list of users from a public API.

// Fetching users from JSONPlaceholder API
fetch('https://jsonplaceholder.typicode.com/users')
  .then(response => {
    if (!response.ok) {
      throw new Error('Network response was not ok');
    }
    return response.json(); // parse JSON body
  })
  .then(data => {
    console.log('Fetched users:', data);
  })
  .catch(error => {
    console.error('Fetch error:', error);
  });

Fetched users: [ { id: 1, name: 'Leanne Graham', ... }, ... ]

Question:

What does response.ok check for?

Answer: It checks whether the HTTP status is in the range 200–299. If not, the request is considered unsuccessful.

Example 2: POST Request Using Fetch

Now let's send data to the server using a POST request.

// Posting data to JSONPlaceholder API
const postData = {
  title: 'Hello Fetch',
  body: 'This is a POST request example.',
  userId: 1
};

fetch('https://jsonplaceholder.typicode.com/posts', {
  method: 'POST',
  headers: {
    'Content-Type': 'application/json'
  },
  body: JSON.stringify(postData)
})
  .then(response => response.json())
  .then(data => {
    console.log('POST success:', data);
  })
  .catch(error => {
    console.error('POST error:', error);
  });

POST success: { id: 101, title: 'Hello Fetch', body: 'This is a POST request example.', userId: 1 }

Question:

Why do we use JSON.stringify(postData)?

Answer: The body of a fetch POST request must be a string, so we convert the JavaScript object into a JSON string format before sending.

Handling Fetch Errors

Fetch only throws an error on network failure (like no internet). It won’t reject on HTTP errors like 404 or 500 — so you need to check response.ok manually.

fetch('https://jsonplaceholder.typicode.com/unknown-endpoint')
  .then(response => {
    if (!response.ok) {
      throw new Error(`Error: ${response.status}`);
    }
    return response.json();
  })
  .then(data => {
    console.log(data);
  })
  .catch(error => {
    console.error('Handled error:', error.message);
  });

Handled error: Error: 404

Points to Remember

• fetch() always returns a Promise.
• Always handle errors using .catch() or try/catch with async/await.
• Use response.json() to parse the JSON response.
• POST requests require setting the 'Content-Type' to 'application/json'.

Practice Tip

Try using fetch to make GET and POST requests to your own mock API using reqres.in or JSONPlaceholder.