# Lifecycle ## Application Lifecycle You can define the following application lifecycle functions in the **app.js** file.

Attribute	Type	Description	Called When
onCreate	() => void	Listens for application creation.	The application is created.
onShow⁶⁺	() => void	Listens for whether the application is running in the foreground.	The application is running in the foreground.
onHide⁶⁺	() => void	Listens for whether the application is running in the background.	The application is running in the background.
onDestroy	() => void	Listens for application uninstallation.	The application exits.

## Page Lifecycle You can define the following page lifecycle functions in the **.js** file of the page.

Attribute	Type	Description	Called When
onInit	() => void	Listens for page initialization.	Page initialization is complete. This function is called only once in the page lifecycle.
onReady	() => void	Listens for page creation.	A page is created. This function is called only once in the page lifecycle.
onShow	() => void	Listens for page display.	The page is displayed.
onHide	() => void	Listens for page disappearance.	The page disappears.
onDestroy	() => void	Listens for page destruction.	The page is destroyed.
onBackPress	() => boolean	Listens for the back button action.	The back button is touched. true means that the page processes the return logic. false means that the default return logic is used. If no value is returned, the default return logic is used.
onActive()⁵⁺	() => void	Listens for page activation.	The page is activated.
onInactive()⁵⁺	() => void	Listens for page suspension.	The page is suspended.
onNewRequest()⁵⁺	() => void	Listens for a new FA request.	The FA has been started and a new request is received.

The lifecycle functions of page A are called in the following sequence: - Open page A: onInit\(\) -\> onReady\(\) -\> onShow\(\) - Open page B on page A: onHide\(\) - Go back to page A from page B: onShow\(\) - Exit page A: onBackPress\(\) -\> onHide\(\) -\> onDestroy\(\) - Hide page A: onInactive\(\) -\> onHide\(\) - Show background page A on the foreground: onShow\(\) -\> onActive\(\) ![](figures/en-us_image_0000001147417424.png)