TS2722：无法调用可能“未定义”的对象

Question

I have an error TS2722 on object connector in Loopback framework. I don't understand why the connector object could be undefined.

It's a method from my neo4j repository:

async query(cypher: string, params?: any, cb?: any): Promise<any> {
// return await this.dataSource.connector.db.query(cypher, params, cb);

  if (this.dataSource && this.dataSource.connector) {
    return await this.dataSource.connector.execute(cypher, params, function (err: Error, results: any) {
      // return await this.dataSource.connector.db.cypher({ "query": cypher }, function (err: Error, results: any) {
      if (err) return cb(err);
        cb(null, results);
    });
  }
}

I don't understand why. Hope you can help.

Answer 1

because your connector can fail to connect. so typescript knows it and don't allow you to do anything with this object.

first - do you have the @types/neo4j (or equivalent) in your package.json ?

second - you should tell typescript to check if your connector is valid with https://www.typescriptlang.org/docs/handbook/advanced-types.html#user-defined-type-guards

ultimate - this is probably what you really need https://www.typescriptlang.org/docs/handbook/advanced-types.html#instanceof-type-guards