JavasScript Open Local File

I am writing a Figma plugin that uses JavaScript and I need to open a file from the plugin folder. This is not JS on a webpage. I mention that because all the JS examples I can find assume a <input type='file'/>.

The code should look something like this:

function readFile (file: File)
{
    let reader = new FileReader() ;
    reader.onload = () =>
    {
        console.log(reader.result) ;
    }
    reader.readAsText(file) ;
}

readFile(new File("folder/File.xml")) ;