golang自定义返回error

package main
import (
"encoding/json"
"errors"
"fmt"
myerr "github.com/mypractise/errors"
)
func myErr() error {
err := myerr.NewError(2, "err test")
return err
}
func staErr() error {
m := make(map[string]string)
err := json.Unmarshal([]byte(""), m)
if err != nil {
return err
}
return errors.New("aaaaa")
}
func main() {
err1 := staErr()
fmt.Println("------sta err:", err1.Error())
err2 := myErr()
fmt.Println("------my err:", err2.Error(), err2.(*myerr.Error).ErrCode)
}