osfs: add js shim

Signed-off-by: Christian Stewart <christian@paral.in>

Author: paralin

osfs/os.go

@@ -1,3 +1,5 @@
+// +build !js
+
 // Package osfs provides a billy filesystem for the OS.
 package osfs // import "github.com/go-git/go-billy/v5/osfs"
 

osfs/os_js.go

@@ -0,0 +1,23 @@
+package osfs
+
+import (
+	"github.com/go-git/go-billy/v5"
+	"github.com/go-git/go-billy/v5/helper/chroot"
+	"github.com/go-git/go-billy/v5/memfs"
+)
+
+// globalMemFs is the global memory fs
+var globalMemFs = memfs.New()
+
+const (
+	defaultDirectoryMode = 0755
+	defaultCreateMode    = 0666
+)
+
+// OS is a filesystem shim for js.
+type OS struct{}
+
+// New returns a new OS filesystem.
+func New(baseDir string) billy.Filesystem {
+	return chroot.New(globalMemFs, baseDir)
+}

osfs/os_posix.go

@@ -1,4 +1,4 @@
-// +build !plan9,!windows
+// +build !plan9,!windows,!js
 
 package osfs