How to detect first launch in react-native

Your logic should follow this:

class MyStartingComponent extends React.Component {
    constructor(){
        super();
        this.state = {firstLaunch: null};
    }

    componentDidMount(){
        AsyncStorage.getItem("alreadyLaunched").then(value => {
            if(value === null){
                 AsyncStorage.setItem('alreadyLaunched', 'true'); // No need to wait for `setItem` to finish, although you might want to handle errors
                 this.setState({firstLaunch: true});
            }
            else{
                 this.setState({firstLaunch: false});
            }}) // Add some error handling, also you can simply do this.setState({fistLaunch: value === null})
    }

    render(){
       if(this.state.firstLaunch === null){
           return null; // This is the 'tricky' part: The query to AsyncStorage is not finished, but we have to present something to the user. Null will just render nothing, so you can also put a placeholder of some sort, but effectively the interval between the first mount and AsyncStorage retrieving your data won't be noticeable to the user.
       }else if(this.state.firstLaunch === 'true'){
           return <FirstLaunchComponent/>
       }else{
           return <NotFirstLaunchComponent/>
       }
}

Hope it helps.