如果 firestore doc.exists 我如何停止父 function 的执行？

Question

I'm trying to stop the async function if a username is found in the database. I can find existingUsername = true, but handleSignup continues to execute and overwrites existing user data.

async function handleSignup {

    var docRef = db.collection("users").doc(username);
    var existingUsername = false

    docRef.get().then((doc) => {
        if (doc.exists) {
            existingUsername = true
        }
        else {
            existingUsername = false
        }
    })

    if (existingUsername == true) {
        return setError("Username exists") // How do I stop the function handleSignup?
    }

    }
//database code to create user
}

Answer 1

Probably best to use async await with this.

async function handleSignup() {

    const docRef = db.collection("users").doc(username);

    const doc = await docRef.get();

    if (doc.exists === true) {
        throw setError("Username exists")
    }

//database code to create user
}

Answer 2

The rest of the execution happens before the promise return because this is how javascript works.. you should use await or add another then chain. i refactored your code to make it work using await:

 var existingUsername = false

 const doc = await docRef.get();
 const existingUsername = doc.exists();

 if (existingUsername) {
    return setError("Username exists")
 }

//database code to create user