Method _positionOf

src/Map.js:430–458

(key, buildIndex)

  // transient inserts, where the node is reused so the O(n) build amortizes).
  // Persistent inserts already pay an O(n) copy, so a throwaway index is skipped.
  _positionOf(key, buildIndex) {
    const entries = this.entries;
    let index = this._index;
    if (
      index === undefined &&
      buildIndex &&
      entries.length >= MIN_HASH_COLLISION_INDEX_SIZE
    ) {
      index = this._buildIndex();
    }
    if (index !== undefined) {
      const positions = index[hashCollisionKey(key)];
      if (positions !== undefined) {
        for (let jj = 0; jj < positions.length; jj++) {
          const ii = positions[jj];
          if (is(key, entries[ii][0])) {
            return ii;
          }
        }
      }
      return -1;
    }
    for (let ii = 0, len = entries.length; ii < len; ii++) {
      if (is(key, entries[ii][0])) {
        return ii;
      }
    }
    return -1;
  }

  // Builds and memoizes the secondary index. A plain object, not `Map` — which
  // in this module resolves to the *Immutable* Map, not the native one.