关键字 yield 只能在一个生成器中使用。 searchAccountKey 目前是一个正常的功能。您需要在函数名称之前使用 * 使其成为生成器。

  static * searchAccountKey（key，回调）{
 const user = yield User.findBy（'key'，key）
 // ... 
} 
 

此更改后，您需要调用 Lookup.searchAccountKey 与 yield 还。

  yield Lookup.searchAccountKey（...）
 / pre> 
So, I am creating different helpers to reduce some code on my controller. So I created a class called Lookup to help me search for users in my database and I created a searchAccountKey(key, callback). So, whenever I utilize this method it seems to work however the user object returns with nothing instead of the user.

I am suspecting this is happening because of yield but when I do use yield it gives me an error.

LookupHelper.js
'use strict';
const User = use('App/Model/User');
class LookupHelper {
  // Grab the user information by the account key
  static searchAccountKey(key, callback) {
      const user = User.findBy('key', key)
      if (!user) {
        return callback(null)
      }
      return callback(user);
  }

}

module.exports = LookupHelper;
UsersController (line 44)
Lookup.searchAccountKey(account.account, function(user) {
    return console.log(user);
});
EDIT: Whenever I put yield infront of the User.findBy()

The keyword 'yield' is reserved const user = yield User.findBy('key', key)

Code:
'use strict';
const User = use('App/Model/User');
class LookupHelper {
  // Grab the user information by the account key
  static searchAccountKey(key, callback) {
      const user = yield User.findBy('key', key)
      if (!user) {
        return callback(null)
      }
      return callback(user);
  }

}

module.exports = LookupHelper;

The keyword yield can be only used inside a generator. searchAccountKey is currently a normal function. You need to use * before the name of the function to make it a generator.
static * searchAccountKey (key, callback) {
  const user = yield User.findBy('key', key)
  // ...
}
After this change you will need to call Lookup.searchAccountKey with yield also.
yield Lookup.searchAccountKey(...)