Why there is no userID? it is undefined - reactjs

Question

Hello my friends i am trying to save data to firebase while using userID However i could not make it ! Please can anyone help me ?
class ImportScreen extends Component {
writeuserdata( name, surname, age, userId) {
firebase.database().ref('Users/' + userId).set({
name,
surname,
age
}).then((data) => {
console.log('data', data)
}).catch ((error) => {
console.log('eror',error)
})
}
render() {
return (
<View style={{ flex: 1, alignItems: 'center', justifyContent: 'center', backgroundColor: 'white' }}>
<TextInput
placeholder="Enter a name"
onChangeText={(name) => this.setState({ name })}
/>
<TextInput
placeholder="Enter a surname"
onChangeText={(surname) => this.setState({ surname })}
/>
<TextInput
placeholder="Enter age"
onChangeText={(age) => this.setState({ age })}
/>
<Button
title="Save"
onPress={() => this.writeuserdata(this.state.name, this.state.surname, this.state.age)} />
</View>
);
}
}
enter image description here

Answer 1

You're calling writeuserdata with:
this.writeuserdata(this.state.name, this.state.surname, this.state.age)}
Since writeuserdata expects 4 parameters, and you're only passing 3, the 4th argument is going to be undefined.
If you want to also pass the UID of the current Firebase Authentication user, that'd be something like:
this.writeuserdata(this.state.name, this.state.surname, this.state.age, firebase.auth().currentUser.uid)}