How to Convert cURL Command to JavaScript Fetch: Complete Guide (2026)

async function getUsers() {
  try {
    const response = await fetch('https://api.example.com/users');

    if (!response.ok) {
      throw new Error(`HTTP error! status: ${response.status}`);
    }

    const data = await response.json();
    console.log(data);
    return data;
  } catch (error) {
    console.error('Fetch failed:', error);
  }
}

getUsers();

async function createUser(userData) {
  const response = await fetch('https://api.example.com/users', {
    method: 'POST',
    headers: {
      'Content-Type': 'application/json',
      'Accept': 'application/json',
    },
    body: JSON.stringify(userData),
  });

  if (!response.ok) {
    const errorBody = await response.text();
    throw new Error(`Request failed ${response.status}: ${errorBody}`);
  }

  return response.json();
}

// Usage
createUser({ name: 'Alice', email: 'alice@example.com' })
  .then(user => console.log('Created:', user))
  .catch(err => console.error(err));

// URL-encoded form data
// cURL: curl -d "username=alice&password=secret" https://api.example.com/login

const params = new URLSearchParams();
params.append('username', 'alice');
params.append('password', 'secret');

const response = await fetch('https://api.example.com/login', {
  method: 'POST',
  headers: {
    'Content-Type': 'application/x-www-form-urlencoded',
  },
  body: params.toString(),
});

// --- OR for multipart form data (file uploads) ---
// cURL: curl -F "avatar=@/path/to/photo.jpg" -F "userId=123" https://api.example.com/upload

const formData = new FormData();
formData.append('avatar', fileInput.files[0]); // File object from <input type="file">
formData.append('userId', '123');

// NOTE: Do NOT set Content-Type header when using FormData.
// The browser sets it automatically with the correct boundary.
const uploadResponse = await fetch('https://api.example.com/upload', {
  method: 'POST',
  body: formData,
});

// cURL: curl --max-time 10 https://api.example.com/slow-endpoint

async function fetchWithTimeout(url, options = {}, timeoutMs = 10000) {
  const controller = new AbortController();
  const timeoutId = setTimeout(() => controller.abort(), timeoutMs);

  try {
    const response = await fetch(url, {
      ...options,
      signal: controller.signal,
    });
    clearTimeout(timeoutId);
    return response;
  } catch (error) {
    clearTimeout(timeoutId);
    if (error.name === 'AbortError') {
      throw new Error(`Request timed out after ${timeoutMs}ms`);
    }
    throw error;
  }
}

// Usage
const response = await fetchWithTimeout(
  'https://api.example.com/slow-endpoint',
  { headers: { 'Authorization': 'Bearer TOKEN' } },
  10000 // 10 seconds
);

// Sending cookies/credentials cross-origin
// cURL: curl --cookie "session=abc" https://api.otherdomain.com/data

const response = await fetch('https://api.otherdomain.com/data', {
  credentials: 'include', // Send cookies with cross-origin requests
});

// Options for credentials:
// 'omit'    - never send cookies (default for cross-origin)
// 'same-origin' - send cookies only for same-origin requests (default)
// 'include' - always send cookies (requires server CORS: Access-Control-Allow-Credentials: true)

curl -X POST https://api.stripe.com/v1/charges \
  -H "Authorization: Bearer sk_test_abc123" \
  -H "Content-Type: application/x-www-form-urlencoded" \
  -H "Stripe-Version: 2023-10-16" \
  -d "amount=2000" \
  -d "currency=usd" \
  -d "source=tok_visa" \
  -d "description=Charge for alice@example.com"

async function createCharge({ amount, currency, source, description }) {
  const params = new URLSearchParams({
    amount: String(amount),
    currency,
    source,
    description,
  });

  const response = await fetch('https://api.stripe.com/v1/charges', {
    method: 'POST',
    headers: {
      'Authorization': 'Bearer sk_test_abc123',
      'Content-Type': 'application/x-www-form-urlencoded',
      'Stripe-Version': '2023-10-16',
    },
    body: params.toString(),
  });

  if (!response.ok) {
    const error = await response.json();
    throw new Error(`Stripe error: ${error.error?.message}`);
  }

  return response.json();
}

// Usage
const charge = await createCharge({
  amount: 2000,
  currency: 'usd',
  source: 'tok_visa',
  description: 'Charge for alice@example.com',
});
console.log('Charge created:', charge.id);