箭頭函數報錯：Add @babel/plugin-proposal-class-properties (https://git.io/vb4SL) to the 'plugins' section of your Babel config to enable transformation.

解決：根目錄新建babel.config.js加入如下內容

module.exports = {
    presets: [ "@babel/preset-env", "@babel/preset-react" ],
    plugins: [ "@babel/plugin-transform-arrow-functions", "@babel/plugin-proposal-class-properties" ]
}