Javascript 函数返回 true/false 返回 undefined

Question

I currently have a problem with my function. I'm using a MongoDB Database to check is something exists and as you can see, if a data value is true, I wanna set the return value of the function to false or when it's wrong it should return false.

Everything works to this point. The function is just returning "undefined". I tried everything I could think of and tested atleast one hour but couldn't find any solution.

I hope anyone of you guys could help me to return a true or false here. Thanks for your help:D

Note: Also tried it with async before, didn't work out

function CheckActiveGamesPlayer1(memberid) {
            console.log("3")
            db.findOne({ GuildID: guild.id, Player1: memberid }, async(err, data) => {
                if (data.Ingame === true) {
                    console.log("4")
                    Embed.setDescription(`<@${memberid}> is in an active game. Can't start the game!`).setColor("RANDOM");
                    channel.send({ embeds: [Embed], ephemeral: true })
                    return false;
                } else {
                    console.log("5")
                    return true;
                }

            })

        }

Answer 1

That is because you aren't actually returning anything in CheckActiveGamesPlayer1 . However, you are returning something in your db.findOne callback.

I am not sure how you are calling the CheckActiveGamesPlayer1 function, but I would suggest returning a Promise so you can either await or .then it to get the response you're after.

function CheckActiveGamesPlayer1(memberid) {
  console.log('3');
  return new Promise( (resolve, reject) => {
    db.findOne({ GuildID: guild.id, Player1: memberid }, async (err, data) => {
      if (data.Ingame === true) {
        console.log('4');
        Embed.setDescription(`<@${memberid}> is in an active game. Can't start the game!`).setColor('RANDOM');
        channel.send({ embeds: [Embed], ephemeral: true });
        resolve(false);
      } else {
        console.log('5');
        resolve(true);
      }
    });
  });
}

You can then call your function and get the response by .then

IE:

CheckActiveGamesPlayers1(1).then( result => console.log(result) );

You can also add async to your CheckActivePlayers1 function so you can just await it.

IE:

async function CheckActiveGamesPlayer1(memberid) { ... }
const result = await CheckActiveGamesPlayers1(1);

I am not sure which version of mongo you are working with. But there's a chance you can just return db.findOne as long as that returns a promise. The way you are currently using db.findOne is in the form of a callback, so there would be some code re-arranging if you went this route.

https://www.mongodb.com/docs/drivers/node/current/usage-examples/findOne/

Answer 2

Try something like this. db.findOne probably returns a promise, so you can do await db.findOne instead of providing a callback, then you can return like normal after that.

async function CheckActiveGamesPlayer1(memberid) {
    console.log("3")
    const data = await db.findOne({ GuildID: guild.id, Player1: memberid });
    if (data.Ingame === true) {
        console.log("4")
        Embed.setDescription(`<@${memberid}> is in an active game. Can't start the game!`).setColor("RANDOM");
        channel.send({ embeds: [Embed], ephemeral: true })
        return false;
    } else {
        console.log("5")
        return true;
    }
}

Answer 3

This is not an async function. Your function runs first, returns with undefined. Then, the async callback is called but that value is passed to nothing.

One way to fix this is to make this an async function, then use "await" keyword.