@apollo/query-planner/src/utilities/MultiMap.ts

Apollo Query Planner

export class MultiMap<K, V> extends Map<K, V[]> {
  add(key: K, value: V): this {
    const values = this.get(key);
    if (values) {
      values.push(value);
    } else {
      this.set(key, [value]);
    }
    return this;
  }
}