Array.filter (again)

Keep only items that pass a test — with richer predicates and both callback styles.

Phase 10 introduced filter. Here we stress that the original array is unchanged, show compound tests, and write callbacks as both a function expression and an arrow.

Lengths: original 0 kept 0

Before

    After (new array)

      Apply a filter to compare lengths and lists.

      Important JavaScript

      const kept = players.filter(function (player) {
  const scoreOk = player.score >= minScore;
  const categoryOk = category === "any" || player.category === category;
  const activeOk = activeOnly ? player.active : true;
  return scoreOk && categoryOk && activeOk;
});

// Same idea with an arrow
const keptArrow = players.filter((player) => {
  return player.score >= minScore && player.active;
});

// Original length unchanged; kept may be shorter (even empty).