aureooms/js-merging

export function* iterables ( compare , A , B ) {

    A = A[Symbol.iterator]( ) ;
    B = B[Symbol.iterator]( ) ;

    let _a = A.next( ) ;

    if ( _a.done ) { yield* B ; return ; }

    let a = _a.value ;

    let _b = B.next( ) ;

    if ( _b.done ) { yield a ; yield* A ; return ; }

    let b = _b.value ;

    while ( true ) {

        // <= makes merge stable
        if ( compare( a , b ) <= 0 ) {

            yield a ;

            _a = A.next( ) ;

            if ( _a.done ) {

                yield b ;
                yield* B ;
                return ;

            }

            a = _a.value ;

        }

        else {

            yield b ;

            _b = B.next( ) ;

            if ( _b.done ) {

                yield a ;
                yield* A ;
                return ;

            }

            b = _b.value ;

        }

    }

}