babel loose mode warning

[JakeSidSmith]

Though the "loose" option was set to "false" in your @babel/preset-env config, it will not be used for @babel/plugin-proposal-private-methods since the "loose" mode option was set to "true" for @babel/plugin-proposal-class-properties.
The "loose" option must be the same for @babel/plugin-proposal-class-properties, @babel/plugin-proposal-private-methods and @babel/plugin-proposal-private-property-in-object (when they are enabled): you can silence this warning by explicitly adding
        ["@babel/plugin-proposal-private-methods", { "loose": true }]
to the "plugins" section of your Babel config.

[JakeSidSmith]

https://2ality.com/2015/12/babel6-loose-mode.html