Ember.js Observable decrementProperty() Method

import Route from '@ember/routing/route';
import EmberObject from '@ember/object';

export default class WebsitesRoute extends Route {

    temp;
    model() {
        return "Increment Property";
    }
    setupController(controller, model) {
        super.setupController(controller, model);
        // controller.set('food', this.food);
        controller.set('temp', this.temp);
        controller.set('temp2', this.temp2);
    }
}

import Ember from 'ember';
import EmberObject from '@ember/object';

const Student = EmberObject.extend({
    toStringExtension() {
        return this.get('food');
    }
});
export default Ember.Controller.extend({
    class: 10,
    age: 15,
    student: [
        Student.create({
            Name: 'Aarbh',
            class: 12,
            age: 18,
        }),
        Student.create({
            Name: 'viky',
            class: 9,
            age: 15,
        }),
        Student.create({
            Name: 'Chiku',
            class: 8,
            age: 11,
        }),
        Student.create({
            Name: 'Nikki',
            class: 11,
            age: 17,
        }),
        Student.create({
            Name: 'Ankit',
            class: 8,
            age: 14,
        }),
        Student.create({
            Name: 'Sonam',
            class: 11,
            age: 17,
        }),
        Student.create({
            Name: 'Ravi',
            class: 10,
            age: 16,
        }),
    ],
    actions: {
        older(data) {
            this.incrementProperty(data);
        },
        younger(data) {
            this.decrementProperty(data);
        },

        addItem(data, data1, data2) {

            let temp = Student.create({
                Name: data,
                class: data1,
                age: data2
            });
            alert(temp.toString() + ' Student Added in list');
            this.student.addObject(temp);
        }
    }
});