Unhandled Promise Rejection : Existing value for key "Favorites" must be of type null or array, revived string - react-native

Question

my problem is quite simple but I'm new to react native dev. I'd like to save multiple elements with AsyncStorage (I'm using react-native-simple-store
a library that works like a wrapper but it's same logic) I want display all items for a key in a list , my code look like this:
constructor(props) {
super(props)
this.state = {
UserInput: "",
}
}
SaveValue = () => {
store.push('Favorites', this.state.UserInput)
Keyboard.dismiss()
};
FetchValue = () => {
store.get('Favorites').then((value) => {
this.setState({
favs: value
});
}).done();
};
Same thing with AsynStorage, it just update the item which is not my goal, I'd like to add a new one
SaveValue = () => {
AsyncStorage.setItem("Favorites", this.state.UserInput);
Keyboard.dismiss()
};
FetchValue = () => {
AsyncStorage.getItem("Favorites").then((value) => {
this.setState({
favs: value
});
}).done();
};
This part is my view where I try to display data, you can also see that I use a text input and two buttons one to save and the other to display an array of items stored
render() {
return (
<View>
<TextInput
onChangeText={(UserInput) => this.setState({UserInput})}
placeholder= "Type something"
value={this.state.UserInput} />
<TouchableOpacity
onPress={this.SaveValue}>
<Text>Save</Text>
</TouchableOpacity>
<TouchableOpacity
onPress={this.FetchValue}>
<Text>Fetch</Text>
</TouchableOpacity>
<Text>{this.state.favs}</Text>
</View>
);
}
At this point I can see only one item, I tried to figure it out and saw that I have to use another method called push but when I changed save by push it throw me an error
Unhandled Promise Rejection : Existing value for key "Favorites" must be of type null or array, revived string.
Thanks!

Answer 1

it will work :)
renderFavorites = () => {
AsyncStorage.getItem("Favorites").then((favs) => {
favs.map((fav) => {
return (<Text> {fav} </Text>);
});
});
}
render() {
return (
<View>
<TextInput
onChangeText={(UserInput) => this.setState({UserInput})}
placeholder= "Type something"
value={this.state.UserInput} />
<TouchableOpacity
onPress={this.SaveValue}>
<Text>Save</Text>
</TouchableOpacity>
<TouchableOpacity
onPress={this.FetchValue}>
<Text>Fetch</Text>
</TouchableOpacity>
{this.renderFavorites()}
</View>
);
}

Answer 2

Solution using JSON:
SaveValue = () => {
const newFavs = [...this.state.favs, this.state.UserInput];
this.setState({ favs: newFavs, UserInput: '' }, () => {
AsyncStorage.setItem("Favorites", JSON.stringify(this.state.favs));
Keyboard.dismiss()
});
};
FetchValue = () => {
AsyncStorage.getItem("Favorites").then((value) => {
this.setState({
favs: JSON.parse(value)
});
}).done();
};