React native: How to validate username and password while submitting - validation

Question

I have validate username and password,if username and password is wrong ,then i want through error like 'Invalid username/password'.if any one know,pls let me know.
async submit() {
//Validating username and password
const { username, password } = this.state;
if(username == ''){
this.setState({error:'Username is required'});
} else if(password == ''){
this.setState({error:'Password is required'});
} else {
this.setState({error: null})
let collection={};
collection.username=this.state.username;
collection.password=this.state.password;
// console.warn(collection);
var url = 'my url';
try {
let response = await fetch(url,
{
method: 'POST', // or 'PUT'
body: JSON.stringify(collection), // data can be `string` or {object}!
headers: new Headers({
'Content-Type': 'application/json'
})
});
let res = await response.text();
// console.warn(res);
if (response.status >= 200 && response.status < 300) {
//Handle success
let accessToken = res;
console.log(accessToken);
//On success we will store the access_token in the AsyncStorage
this.storeToken(accessToken);
// console.warn(accessToken);
//After storing value,it will navigate to home
this.props.navigation.navigate('Home');
} else {
//Handle error
console.log('Success:',response);
let error = res;
throw error;
}
} catch(error) {
console.log("error " + error);
}
}
}
response after giving invalid username/password:
0 {…}
field :password
message :Incorrect username or password.

Answer 1

I have written code like this based on status to validated username/password is correct/wrong.so here am posting code if it is useful for anyone in future.below code is,
if (response.status >= 200 && response.status < 300) {
//Handle success
let accessToken = res;
//On success we will store the access_token in the AsyncStorage
this.storeToken(accessToken);
console.warn(accessToken);
//After storing value,it will navigate to home
this.props.navigation.navigate('Home');
} else {
console.log('Success:',response);
this.setState({error:'Invalid username/password'});
let error = res;
throw error;
}