# Registering a Mini Program Account

For each Mini Program, a Mini Program instance needs to be registered by calling the App method via app.js, to link the lifecycle callback function, error listening function, page not found listening function, and the like.

For specific definitions and usage of the parameters, refer to App Reference Documents.

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

A Mini Program has only one app instance, which is shared to all pages. Developers can obtain the globally unique app instance by using the getApp method, and then obtain data in the app or call a function registered with App by the developers.

// xxx.js
const appInstance = getApp()
console.log(appInstance.globalData) // I am global data