Automatic JSON Body Handling

Learn how ofetch automatically stringifies request bodies and sets content-type headers

ofetch automatically handles JSON request bodies for you. When you pass an object or array as the body option, ofetch will:

1. Stringify it to JSON
2. Set the content-type header to application/json
3. Set the accept header to application/json

Basic Usage

Automatic JSON

import { ofetch } from 'ofetch'

// Object body - automatically stringified
await ofetch('/api/users', {
  method: 'POST',
  body: { name: 'John', age: 30 }
})

Content-Type Detection

ofetch only auto-stringifies when the content is JSON-serializable and you haven’t set a different content-type:

// This will NOT be stringified - custom content-type is respected
await ofetch('/api/text', {
  method: 'POST',
  body: '"Hello"',
  headers: { 'content-type': 'text/plain' }
})

What Gets Stringified?

ofetch considers a value JSON-serializable if it’s:

• A plain object ({})
• An array ([])
• A primitive (string, number, boolean, null)
• An object with a .toJSON() method

The following are not stringified:

• FormData - sent as-is
• URLSearchParams - sent as-is
• Blob - sent as-is
• ArrayBuffer / typed arrays - sent as-is
• ReadableStream - sent as-is

toJSON() Support

If your object has a .toJSON() method, ofetch will automatically call it:

class User {
  constructor(public name: string, private password: string) {}
  
  toJSON() {
    // Password won't be included
    return { name: this.name }
  }
}

// Only sends { name: 'John' }
await ofetch('/api/users', {
  method: 'POST',
  body: new User('John', 'secret123')
})

Form URL Encoded

You can send form-encoded data by setting the content-type:

await ofetch('/api/form', {
  method: 'POST',
  headers: { 'content-type': 'application/x-www-form-urlencoded' },
  body: { username: 'john', password: 'secret' }
})
// Sends: username=john&password=secret

Type Definition

From src/types.ts:27:

body?: RequestInit["body"] | Record<string, any>

The body can be any standard RequestInit body type, or a plain object/array that will be automatically stringified.