In all fairness, considering its a trap it is most probably intended to be used against one of your opponents attacking minion. I got draining shield so i just use that
Enchanted Javelin does not say "opponent's attacking monster" on the card. It only did so on release; all errata since then have changed the effect to allow use on either player's attacking monster.
However, despite the confusing errata, the Japanese text says "opponent." This is one of those cards that runs via Japanese text despite the English wording of the card.