You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: fs.go
    path of file: ./repos/elsa/core/ops
    
    the code of the file until where you have to start completion: package ops

import (
	"encoding/json"
	"io"
	"os"
	"path/filepath"
	"time"

	"github.com/elsaland/elsa/core/options"
	"github.com/elsaland/elsa/util"

	"github.com/elsaland/quickjs"
	"github.com/spf13/afero"
)

type FsDriver struct {
	Perms *options.Perms
	Fs    afero.Fs
}

var _ io.Reader = (*os.File)(nil)

func (fs *FsDriver) ReadFile(ctx *quickjs.Context, path quickj
    
func (fs *FsDriver) Walk(ctx *quickjs.Context, pathDir quickjs.Value) quickjs.Value {

	var files []walkFs

	err := filepath.Walk(pathDir.String(), func(path string, info os.FileInfo, err error) error {

		data := walkFs{
			Name:    info.Name(),
			Size:    info.Size(),
			Mode:    info.Mode(),
			ModTime: info.ModTime(),
			IsDir:   info.IsDir(),
			Path:    path,
		}

		if err != nil {
			util.Check(err)
		}

		files = append(files, data)

		return nil
	})

	if err != nil {
		util.Check(err)
	}

	output, err := json.Marshal(files)
	util.Check(err)
	return ctx.String(string(output))
}