I'm use this function to check Answer. Value of compareAns should return true/false but it return undefined.

Return undefined

Data in firebase

function compareAns(quiz, ansIndex) {
    let ansRef = firebase
        .database()
        .ref("Questions/" + quiz + "/ans/" + ansIndex);
    ansRef.on("value", (snapshot) => {
        if (snapshot.exists()) {
            return snapshot.val().is_correct;
        } else console.log("No data");
    });
}