.babelrc

{
    "presets": [
        "@babel/preset-env",
        "@babel/preset-react"
    ],
    "env": {
        "production": {
            "plugins": [
                "@babel/plugin-proposal-object-rest-spread",
                "styled-jsx/babel",
                [
                    "@babel/plugin-proposal-class-properties",
                    {
                        "loose": true
                    }
                ]
            ]
        },
        "development": {
            "plugins": [
                "@babel/plugin-proposal-object-rest-spread",
                "styled-jsx/babel",
                [
                    "@babel/plugin-proposal-class-properties",
                    {
                        "loose": true
                    }
                ],
                [
                    "@babel/plugin-proposal-private-methods",
                    {
                        "loose": true
                    }
                ],
                [
                    "@babel/plugin-proposal-private-property-in-object",
                    {
                        "loose": true
                    }
                ]
            ]
        },
        "test": {
            "plugins": [
                "@babel/plugin-proposal-object-rest-spread",
                "styled-jsx/babel-test",
                [
                    "@babel/plugin-proposal-class-properties",
                    {
                        "loose": true
                    }
                ]
            ]
        }
    }
}