contact-model-mobx.js

import { toJS, observable } from 'mobx'

class Contact {
  id = 0
  @observable name = ''
  @observable number = ''

  constructor(data) {
    this.name = data.name
    this.number = data.number
  }

  update() {
    // Convert data from observable properties to normal JavaScript primitives
    const contact = toJS(this)
    // Then send it
    fetch(API_URL + '/contacts/' + this.id, {
      body: { contact },
      method: 'PATCH'
     })
  }
}