How to use the automerge.Backend function in automerge

create(keys) {
        const docId = Misc_1.encodeDocId(keys.publicKey);
        log('create', docId);
        const doc = new DocBackend.DocBackend(docId, automerge_1.Backend.init());
        doc.updateQ.subscribe(this.documentNotify);
        // HACK: We set a clock value of zero so we have a clock in the clock store
        // TODO: This isn't right.
        this.clocks.set(this.id, doc.id, { [doc.id]: 0 });
        this.docs.set(docId, doc);
        this.cursors.addActor(this.id, doc.id, Misc_1.rootActorId(doc.id));
        this.initActor(keys);
        return doc;
    }
    // TODO: Temporary solution to replace meta.localActorId

}
                        this.toFrontend.push({
                            type: 'Reply',
                            id,
                            payload: { type: 'MetadataReplyMsg', metadata: payload },
                        });
                    });
                    break;
                }
                case 'MaterializeMsg': {
                    const doc = this.docs.get(query.id);
                    const changes = doc.back
                        .getIn(['opSet', 'history'])
                        .slice(0, query.history)
                        .toArray();
                    const [, patch] = automerge_1.Backend.applyChanges(automerge_1.Backend.init(), changes);
                    this.toFrontend.push({ type: 'Reply', id, payload: { type: 'MaterializeReplyMsg', patch } });
                    break;
                }
            }
        });
        this.receive = (msg) => {

this.bench('applyRemoteChanges', () => {
                const [back, patch] = automerge_1.Backend.applyChanges(this.back, changes);
                this.back = back;
                this.updateClock(changes);
                const history = this.back.getIn(['opSet', 'history']).size;
                this.updateQ.push({
                    type: 'RemotePatchMsg',
                    doc: this,
                    patch,
                    history,
                });
            });
        });