undefined is not a function in React Native - reactjs

Question

I'm trying to make an API call in React Native to handle user authentication. I'm passing this.state.email and this.state.password (both bound to text inputs) to a function in my services/ folder, where the call is made. Afterwards, the screen should navigate to the home stack or return an error. This is my login screen code:
import AuthService from ...
export default class LoginScreen extends Component {
constructor(props) {
super(props);
this.login = this.login.bind(this);
this.state = {
email: '',
password: '',
};
}
login() {
AuthService.login(this.state.email, this.state.password)
.then(this.props.navigation.navigate('Main')) //Move to home screen
.catch(console.error('Error')); //Handle error
}
render() {
return (
<View>
<TextInput
onChangeText={email => this.setState({ email })}
value={this.state.email}
/>
<TextInput
onChangeText={password => this.setState({ password })}
value={this.state.password}
/>
<TouchableOpacity onPress={this.login}>
<Text style={styles.text}>Submit</Text>
</TouchableOpacity>
</View>
);
}
}
And this is my AuthService function:
login(email, password) {
// Check if credentials exist
if (!email || !password) {
return undefined;
}
return fetch(
`${AUTH_ROOT}/login`,
{
method: 'POST',
body: { email, password },
}
.then(
res => {
const data = { ...res.data };
if (!data) {
throw new Error('No user returned from auth service');
}
},
res => {
context.error = 'Could not login';
console.log(res);
}
)
);
},
But I'm getting the error:
> undefined is not a function (near '...{
> method: 'POST',
> body: {
> email: email,
> password: password,
> } }.then...')
What does this mean? Is my call not done correctly?

Answer 1

login(email, password) {
// Check if credentials exist
if (!email || !password) {
return undefined;
}
return fetch(
`${AUTH_ROOT}/login`,
{
method: 'POST',
body: { email, password },
}
)
.then(
res => {
const data = { ...res.data };
if (!data) {
throw new Error('No user returned from auth service');
}
},
res => {
context.error = 'Could not login';
console.log(res);
}
)
},
The right syntax for fetch is
fetch(url, params).then()
instead you had
fetch(url, params.then())