var data = { ...my contact JSON data... }
var url = '/process/contact' // associated script = /src/routes/process/contact.js

fetch(url, {
  method: 'POST',
  body: JSON.stringify(data),
  headers: {
    'Content-Type': 'application/json'
  }
})
.then(r => {
  r.json()
    .then(function(result) {
      // The data is posted: do something with the result...
    })
})
.catch(err => {
  // POST error: do something...
  console.log('POST error', err.message)
})

export async function post(req, res, next) {
  /* Initializes */
  res.setHeader('Content-Type', 'application/json')
  /* Retrieves the data */
  var data = req.body
  // Do something with the data...
  /* Returns the result */
  return res.end(JSON.stringify({ success: true }))
}