Beauty is in the eye of the beholder, I guess.  You'd prefer:
```javascript
      var fastkey = function fastkey(key) {
        var type = typeof key;
        if (type === 'string') {
          return '$' + key;
        } else if (type === 'number' && !Object.is(key, -0)) {
            return key;
        }
        return null;
      };
```