Using the observable decorator, the store obtained by the component is an empty object

I use mobx to manage state in React. After decorating a class with observable decorator, the store object passed to the component through Provider is empty

import {observable} from "mobx"
 class Store{
    @observable a="test"

} 
export default Store
import React from "react";
import ReactDOM from "react-dom";
import "./index.css";
import App from "./mobx/App";
import registerServiceWorker from "./registerServiceWorker";
import {Provider} from "mobx-react"
import Store from "./mobx/store"
let store =new Store()
ReactDOM.render(<Provider store={store}><App/></Provider>, document.getElementById("root"));
registerServiceWorker();
storestore

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Apr.09,2021
MySQL Query : SELECT * FROM `codeshelper`.`v9_news` WHERE status=99 AND catid='6' ORDER BY rand() LIMIT 5
MySQL Error : Disk full (/tmp/#sql-temptable-64f5-1b3b7d0-2c2a6.MAI); waiting for someone to free some space... (errno: 28 "No space left on device")
MySQL Errno : 1021
Message : Disk full (/tmp/#sql-temptable-64f5-1b3b7d0-2c2a6.MAI); waiting for someone to free some space... (errno: 28 "No space left on device")
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