Given the scenarion where:
```javascript
const one = neo4j.int(1)
const two = neo4j.int(2)
```
The following operations was resulting in string concatenation:
```javascript
console.log( one + two ) // '12'
console.log( 1 + one ) // '11'
console.log( one.add(two).toInt() ) // 3, which is correct
console.log( '1' + one) // '11', correct
```
This is issue is solved by defining the method `Integer.valueOf` which defines the primitive type representation.
The primitive representation of `Integer` is set as `BigInt`.
This way:
```javascript
console.log (one + two ) // 3n
console.log ( 1 + one ) // thrown an exception since we can not add bigint to number
console.log ( 1n + one ) // 2n
console.log ( -one ) // -1n
console.log( '1' + one) // '11', correct
```

Co-authored-by: Florent Biville <445792+fbiville@users.noreply.github.com>