HTTP Content-Type & MIME-Types Referenz

// 1. JSON Payload: Explicit Content-Type required
await fetch('/api/submit', {
  method: 'POST',
  headers: { 'Content-Type': 'application/json' },
  body: JSON.stringify({ title: 'Report', priority: 1 }),
});

// 2. File Upload: DO NOT set Content-Type header!
// The browser automatically sets multipart/form-data WITH the unique boundary string
const formData = new FormData();
formData.append('document', fileInput.files[0]);
await fetch('/api/upload', {
  method: 'POST',
  body: formData, // Browser calculates Content-Type + boundary automatically
});