currentPage

controllers.application\.js

import Controller from '@ember/controller';
import { action } from '@ember/object';
import { computed } from '@ember/object';

export default Controller.extend({
//  currentPage = 0;
  _data: 0,

  currentPage: computed({
    get() {
      console.log("get() ", this._data);
      return this.get('_data');
    },
    set(k, value) {
      console.log("set() ", this._data, {k}, {value});
      this.set('_data', value);
      return value;
    }
  }),
  
  actions: {
    increment() {
      console.log(this.get('currentPage'));
      this.set('currentPage', this.get('currentPage') + 1);
    }
  }
});

templates.application\.hbs

Current page is: {{this.currentPage}}

<button type="button" {{action "increment"}}>
  Increment
</button>

twiddle\.json

{
  "version": "0.17.1",
  "EmberENV": {
    "FEATURES": {},
    "_TEMPLATE_ONLY_GLIMMER_COMPONENTS": false,
    "_APPLICATION_TEMPLATE_WRAPPER": true,
    "_JQUERY_INTEGRATION": true
  },
  "options": {
    "use_pods": false,
    "enable-testing": false
  },
  "dependencies": {
    "jquery": "https://cdnjs.cloudflare.com/ajax/libs/jquery/3.5.1/jquery.js",
    "ember": "3.18.1",
    "ember-template-compiler": "3.18.1",
    "ember-testing": "3.18.1"
  },
  "addons": {
    "@glimmer/component": "1.0.0",
    "ember-data": "3.18.0"
  }
}