Why use mobx gist 2

gist.js

class ResourceStore {
  @observable
  resources = {};
 
  @action("REQUEST_RESOURCE")
  requestResource(id) {
    this.resources[id] = {loading:true};
    return fetch(`url/resource/${id}`)
        .then(response=>response.json())
        .then(action("REQUEST_RESOURCE_SUCCESS",
              resource=>{this.resources[id] = {loading:false,resource};}))
        .catch(action("REQUEST_RESOURCE_FAILURE",
              error=>{this.resources[id] = {loading:false,error};}))
  }
}