Method toJSON

modules/core/EditSystem.js:898–994

* toJSON * Save the edit history to JSON. * @return {string?} A String containing the JSON, or `undefined` if nothing to save

()

   * @return  {string?}  A String containing the JSON, or `undefined` if nothing to save
   */
  toJSON() {
    if (!this.hasChanges()) return;

    const OSM_PRECISION = 7;
    const baseGraph = this.base.graph;   // The initial unedited graph
    const modifiedEntities = new Map();  // Map(Entity.key -> Entity)
    const baseEntities = new Map();      // Map(entityID -> Entity)
    const historyData = [];

    // Preserve the users history of edits..
    for (const edit of this._history) {
      const modified = [];
      const deleted = [];

      // watch out: for modified entities we index on "key" - e.g. "n1v1"
      for (const [entityID, entity] of edit.graph.local.entities) {
        if (entity) {
          const key = osmEntity.key(entity);
          modifiedEntities.set(key, _copyEntity(entity));
          modified.push(key);
        } else {
          deleted.push(entityID);
        }

        // Collect the original versions of edited Entities.
        const original = baseGraph.hasEntity(entityID);
        if (original && !baseEntities.has(entityID)) {
          baseEntities.set(entityID, _copyEntity(original));
        }

        // For modified ways, collect originals of child nodes also. - iD#4108
        // (This is needed for situations where we connect a way to an existing node)
        if (entity && entity.nodes) {
          for (const childID of entity.nodes) {
            const child = baseGraph.hasEntity(childID);
            if (child && !baseEntities.has(child.id)) {
              baseEntities.set(child.id, _copyEntity(child));
            }
          }
        }

        // Collect original parent ways also.
        // (This is needed for situations where we reshape or move a way -
        //  behind the scenes, only the nodes were really modified)
        if (original) {
          for (const parent of baseGraph.parentWays(original)) {
            if (!baseEntities.has(parent.id)) {
              baseEntities.set(parent.id, _copyEntity(parent));
            }
          }
        }
      }

      const sources = edit.sources ?? {};

      const item = {};
      if (modified.length)   item.modified = modified;
      if (deleted.length)    item.deleted = deleted;