public static function is_json($st)
  {
    if ( \is_string($st) && !empty($st) &&
      ( (substr($st, 0, 1) === '{') || (substr($st, 0, 1) === '[') )){
      json_decode($st);
      return (json_last_error() == JSON_ERROR_NONE);
    }
    return false;
  }
public static function is_json($st)
  {
    if ( \is_string($st) && !empty($st) &&
      ( (substr($st, 0, 1) === '{') || (substr($st, 0, 1) === '[') )){
      json_decode($st);
      return (json_last_error() == JSON_ERROR_NONE);
    }
    return false;
  }
public static function is_json ( $ st ) { if ( \ is_string ( $ st ) && ! empty ( $ st ) && ( ( substr ( $ st , 0 , 1 ) === '{' ) || ( substr ( $ st , 0 , 1 ) === '[' ) ) ) { json_decode ( $ st ) ; return ( json_last_error ( ) == JSON_ERROR_NONE ) ; } return false ; }
Checks if the string is a json string.

```php
\bbn\x::dump(\bbn\str::is_json('{"firstName": "John", "lastName": "Smith", "age": 25}'));
// (bool) true
```

@param string $st The string.
@return bool
Checks if the string is a json string .