Merge and sync

AssetStore.js

    // assets param is either a plain js object or an array of plain js objects
    _merge(assets) {
        // If parameter is a single object, make it an array
        assets = Array.isArray(assets) ? assets : [assets];
        
        // From object(s), create an ordered map of id => record
        let newAssets = new OrderedMap(assets.map(asset => [asset.id, new Asset(asset)]));

        // Merge in new assets, keeping old if new is equal (same values) to preserve reference equality
        this._assets = this._assets.mergeWith((prev, next) => prev.equals(next) ? prev : next, newAssets);
        
        // Return updated list of assets as well as new assets to enable sync
        return { currentAssets: this._assets, newAssets };
    }

    _sync(assets) {
        let { currentAssets, newAssets } = this._merge(assets);
        
        // Remove assets in updated list that are not in old list, i.e., remove assets that have been deleted
        return this._assets = currentAssets.filter(asset => newAssets.has(asset.id));
    }

//...

        case ActionTypes.ASSET_RECEIVE_ALL:
            assetStore._sync(action.data);
            assetStore.emitChange();
            break;
        case ActionTypes.ASSET_RECEIVE_CREATED:
        case ActionTypes.ASSET_RECEIVE_UPDATED:
            assetStore._merge(action.data);
            assetStore.emitChange();
            break;