Convert curl to JavaScript Fetch API

Converting curl to JavaScript Fetch

The Fetch API is the modern standard for making HTTP requests in JavaScript, available in all browsers and Node.js 18+. Converting curl to fetch is essential for frontend and full-stack developers.

GET Request

curl:

curl https://api.example.com/users

JavaScript:

const response = await fetch("https://api.example.com/users");
const data = await response.json();

POST with JSON

curl:

curl -X POST https://api.example.com/users \
  -H "Content-Type: application/json" \
  -d '{"name": "Alice"}'

JavaScript:

const response = await fetch("https://api.example.com/users", {
  method: "POST",
  headers: { "Content-Type": "application/json" },
  body: JSON.stringify({ name: "Alice" }),
});
const data = await response.json();

Bearer Token Authentication

curl:

curl -H "Authorization: Bearer token123" https://api.example.com/me

JavaScript:

const response = await fetch("https://api.example.com/me", {
  headers: { "Authorization": "Bearer token123" },
});

Error Handling

Unlike curl, fetch does not reject on HTTP error status codes. You must check response.ok manually:

const response = await fetch("https://api.example.com/data");
if (!response.ok) {
  throw new Error(`HTTP ${response.status}: ${response.statusText}`);
}
const data = await response.json();

Key Differences from curl

curl behavior	fetch equivalent
Auto-follows redirects	redirect: "follow" (default)
-X METHOD	method: "METHOD"
-H "Key: Value"	headers: { "Key": "Value" }
-d 'body'	body: "string"
-u user:pass	headers: { "Authorization": "Basic " + btoa("user:pass") }
Cookie handling	credentials: "include"
Timeout	AbortSignal.timeout(ms)

Abort and Timeout

const response = await fetch("https://api.example.com/data", {
  signal: AbortSignal.timeout(5000),
});

Fetch provides a clean, promise-based API that integrates naturally with modern async/await JavaScript patterns.