Introduce dedicated custom error types for improved user-experience

js/modules/k6/experimental/fs/errors.go

@@ -0,0 +1,51 @@
+package fs
+
+import "fmt"
+
+// NewError creates a new Error object of the provided kind and with the
+// provided message.
+func NewError(k ErrorKind, message string) *Error {
+	return &Error{
+		Name:    k,
+		Message: message,
+	}
+}
+
+// ErrorKind is a type alias for the kind of an error.
+//
+// Note that this is defined as a type alias, and not a binding, so
+// that it is not interpreted as an object by goja.
+type ErrorKind = string
+
+const (
+	// NotFoundError is emitted when a file is not found.
+	NotFoundError ErrorKind = "NotFoundError"
+
+	// InvalidResourceError is emitted when a resource is invalid: for
+	// instance when attempting to open a directory, which is not supported.
+	InvalidResourceError ErrorKind = "InvalidResourceError"
+
+	// ForbiddenError is emitted when an operation is forbidden.
+	ForbiddenError ErrorKind = "ForbiddenError"
+
+	// TypeError is emitted when an incorrect type has been used.
+	TypeError ErrorKind = "TypeError"
+)
+
+// Error represents a custom error object emitted by the fs module.
+type Error struct {
+	// Name contains the name of the error as formalized by the [ErrorKind]
+	// type.
+	Name ErrorKind `json:"name"`
+
+	// Message contains the error message as presented to the user.
+	Message string `json:"message"`
+}
+
+// Ensure that the Error type implements the Go `error` interface.
+var _ error = (*Error)(nil)
+
+// Error implements the Go `error` interface.
+func (e *Error) Error() string {
+	return fmt.Sprintf(e.Name)
+}