# App(Object object)

Sign up for the Mini Program. Take one. Object Parameter that specifies the lifecycle callbacks of Mini Programs, and so on.

App() Must be app.js Must be called and can be called only once. Or there will be unforeseen consequences.

# parameter

# Object object

attribute	type	Required	Introductions	Minimum version
onLaunch	function	no	Lifecycle callbackMonitor Mini Program initialization.
onShow	function	no	Lifecycle callbackMonitor Mini Program start or cut the foreground.
onHide	function	no	Lifecycle callbackListen to the Mini Program cut background.
onError	function	no	Error listener.
onPageNotFound	function	no	There is no listener function on the page.	1.9.90
onUnhandledRejection	function	no	Untreated Promise Rejects event listener functions.	2.10.0
onThemeChange	function	no	Monitor subject changes	2.11.0
Other	any	no	Developers can add any function or data variable to `Object` Parameter, with the `this` Can access

For the definition of Mini Programs and the mechanism for running Mini Programs, see[Operation mechanism]((runtime/Operation-mechanism).

# sample code

App({
  onLaunch (options) {
    // From the something initial when launch.
  },
  onShow (options) {
    // From the something when show.
  },
  onHide () {
    // From the something when hide.
  },
  onError (msg) {
    console.log(msg)
  },
  globalData: 'I on the global data'
})

# onLaunch(Object object)

Mini Program initialization is completed when the trigger, the global trigger only once. Parameters can also be used wx.getLaunchOptionsSync Get.

parameter: With wx.getLaunchOptionsSync Agreement

# onShow(Object object)

Mini Program start, or from the background into the foreground triggered when the display. You can also use wx.onAppShow Bind listening.

parameter: With wx.onAppShow Agreement

# onHide()

Triggered when the Mini Program enters the background from the foreground. You can also use wx.onAppHide Bind listening.

# onError(String error)

Script error or API Triggered on an error call. You can also use wx.onError Bind listening.

parameter: With wx.onError Agreement

# onPageNotFound(Object object)

Start from base library version 1.9.90. Please remaining backward compatible.

Triggered when the page the Mini Program is trying to open does not exist. You can also use wx.onPageNotFound Bind listening. Attention please refer to wx.onPageNotFound。

parameter: With wx.onPageNotFound Agreement

Sample code:

App({
  onPageNotFound(res) {
    wx.redirectTo({
      url: 'pages/...'
    }) // If it were Tabs Page, use the wx.switchTab
  }
})

# onUnhandledRejection(Object object)

Start from base library version 2.10.0. Please remaining backward compatible.

Mini Programs have unhandled Promise Triggered when rejected. You can also use wx.onUnhandledRejection Bind listening. Attention please refer to wx.onUnhandledRejection。

parameter: With wx.onUnhandledRejection Agreement

# onThemeChange(Object object)

Start from base library version 2.11.0. Please remaining backward compatible.

Triggered when the system switches topics. You can also use wx.onThemeChange Bind listening.

parameter: With wx.onThemeChange Agreement