undefined not an object ->react native JS - react-native

Question

my Code is:
import Note from './Note';
export default class Main extends React.Component {
constructor(props) {
super(props);
this.state = {
noteArray: [],
noteText: '',
}
}
render() {
let notes = this.state.noteArray.map((val, key)=>{
return <Note key={key} keyval={key} val={val}
deleteMethod={()=>this.deleteNote(key)}></Note>
});
return (
<View style={styles.container}>
<View style={styles.header}>
<Text style={styles.headerText}>Yapılacaklar Listesi</Text>
</View>
<ScrollView style={styles.scrollContainer}>
{notes}
</ScrollView>
<View style={styles.footer}>
<TextInput
style={styles.textInput}
placeholder='Notunuz...'
placeholderTextColor='white'
underlineColorAndroid='transparent'
onChangeText={(noteText)=> this.setState({noteText})}
value={this.state.noteText}>
</TextInput>
</View>
<TouchableOpacity onPress={ this.addNote.bind(this) } style={styles.addButton} >
<Text style={styles.addButtonText}>+</Text>
</TouchableOpacity>
</View>
);
}
addNote()
{
if (this.state.noteText){
var d=new Date;
this.state.noteArray.push({
'date':d.getFullYear()
+'/'+(d.getMonth()+1)
+'/'+d.getDate()
});
this.setState({ noteArray: this.state.NoteArray })
this.setState({ noteText: '' })
}
}
}
My error is:undefined not an object (evaluating 'this.state.noteArray.map')
how can i solve this?
i started learn react. The error's screen is
Error Screen
it's my first example. :)

Answer 1

You have to make sure your array is existent:
let notes = !!this.state.noteArray && this.state.noteArray.map((val, key)=>{
should do the job.
The !! is a double negation to avoid another typical error.
This way if noteArray doesn´t exist, the second part after the && is not executed. You could go further and add security checks like checking that it actually is an array etc. but with the above line it should work as long as you actually have an array.