IPhone : How to call AlertIOS in React Native

I am a iOS developer, but I know a a little javascript. I am trying to use the AlertIOS, the document api is this static alert(title: string, message?: string, buttons?: Array<{ text: ?string; onPress: ?Function; }>)

I am confused with the paras. I tried to write like this, but it says it's wrong. AlertIOS('Username empty', 'Please type your username', buttons: {{text: 'Cancel', onPress: onPressCancel}});

Could anyone explain me how to call this function and the syntax?