You can inject build time constants in compiled code with @rollup/plugin-replace.

Something like this:

rollup.config.js

import replace from '@rollup/plugin-replace'

...



const production = !process.env.ROLLUP_WATCH



export default {

  ...

  plugins: [

    replace({

      'process.env': production ? '"production"' : '"dev"',

    }),

    ...

  ]

}

Note the double quotes of the value: '"production"'. The plugin injects the string as is in the code so, if you want a string, you need quotes in the quotes.

Also, as mentioned in the plugin's docs, it should be put at the beginning of your plugins array to enable optimizations like shaking out dead code by other plugins that follows it.