Loop to find all left and right part of the string
for ( let i = 0 ; i < l - 1 ; i ++ ) { let left = s . substring ( 0 , i + 1 ) ; let right = s . substring ( i + 1 ) ; let x = parseInt ( left ) ; let y = parseInt ( right ) ; if ( ! isPrime ( x + y ) ) return false ; } return true ; }