Dynamic Sparse Array Index Mapping and Mutation Tracking in Svelte

export class SparseIndexMap {
  constructor() {
    this.dense = [];
    this.sparse = [];
  }
  insert(key, value) {
    const idx = this.dense.length;
    this.dense.push({ key, value });
    this.sparse[key] = idx;
  }
  get(key) {
    const idx = this.sparse[key];
    return idx !== undefined && this.dense[idx]?.key === key ? this.dense[idx].value : undefined;
  }
  remove(key) {
    const idx = this.sparse[key];
    if (idx === undefined || this.dense[idx]?.key !== key) return false;
    const last = this.dense.pop();
    if (idx < this.dense.length) {
      this.dense[idx] = last;
      this.sparse[last.key] = idx;
    }
    delete this.sparse[key];
    return true;
  }
}