That’s not how to create a solid-file-client object.
In a nodejs script using ES6 :
import auth from 'solid-auth-cli'
import FileClientObejct from 'solid-file-client'
const myFileClient = new FileClientObject( auth )
myFileClient.readFile( someURI ).then( response=>{ ... } )
In a browser script:
<script src="solid-auth-client.bundle.js"></script>
<script src="solid-file-client.bundle.js"></script>
<script>
const myFileClient = new SolidFileClient(solid.auth)
myFileClient.readFile( someURI ).then( response=>{ ... } )