Simple binary search algorithm
function binarySearch ( arr , l , r , x ) { if ( r >= l ) { let mid = l + Math . floor ( ( r - l ) / 2 ) ; if ( arr [ mid ] == x ) return mid ; if ( arr [ mid ] > x ) return binarySearch ( arr , l , mid - 1 , x ) ; return binarySearch ( arr , mid + 1 , r , x ) ; } return - 1 ; }