回答

还可以使用mitt.js通过消息订阅的方式来实现。

在util新建文件mitt.js

function mitt(all) {
  all = all || Object.create(null);

  return {
    on(type, handler) {
      (all[type] || (all[type] = [])).push(handler);
    },
    off(type, handler) {
      if (all[type]) {
        all[type].splice(all[type].indexOf(handler) >>> 0, 1);
      }
    },
    emit(type, evt) {
      (all[type] || []).slice().map((handler) => {
        handler(evt);
      });
      (all['*'] || []).slice().map((handler) => {
        handler(type, evt);
      });
    }
  };
}

module.exports = {
  mitt: mitt
}

app.js的代码增加：

const mitt = require('./utils/mitt').mitt

App({
   
    onLaunch: function () {
        let that = this
        that.globalData.bus = mitt()
  
     
        //调用page里的_custommethod
       that.globalData.bus.emit('_custommethod', data)
        
     
    }
  
})

const app = getApp()

Page({
 
    custommethod: function(data){
        
    },
    onShow: function () {
        let that = this
        app.globalData.bus.on('_custommethod', that.custommethod)
       
    },
    onHide: function () {
        let that = this
        app.globalData.bus.off('_custommethod', that.custommethod)
        
    },
   
})