Ember.js Controller addObserver() Method

Ember.js is an open-source JavaScript framework used for developing large client-side web applications which is based on Model-View-Controller (MVC) architecture. Ember.js is one of the most widely used front-end application frameworks. It is made to speed up development and increase productivity. Currently, it is utilized by a large number of websites, including Square, Discourse, Groupon, Linked In, Live Nation, Twitch, and Chipotle.

The addObserver() method registers an observer to the property and the Observer notify whenever the value of the property changes. 

Syntax:

addObserver( key, target, method, sync );

Parameters: 

• key: It is the key on which the observer will register. 
• target: It is the target object which will invoke property change. 
• method: It is the target method that will invoke property change.
• sync: It describes whether the observer is synced or not. 

Return: Observable

Steps to Install and Run Ember.js:

Step 1: To run the following examples you will need to have an ember project with you. To create one, you will need to install ember-cli first. Write the below code in the terminal:

npm install ember-cli

Step 2: Now you can create the project by typing in the following piece of code:

ember new <project-name> --lang en

To start the server, type:

ember serve

Example 1: Type the following code to generate the route for this example:

ember generate route addObserver1

app/routes/addObserver1.js

Javascript

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

export default class StudentsRoute extends Route {
    p1 = [
        'Digital Camera',
        'Jugs, cups & straws',
        'Balloons',
        'Scissors',
        'Cold Drink',
        'Table',
    ];
    model() {
        return this.p1;
    }
    setupController(controller, model) {
        super.setupController(controller, model);
        controller.set('p1', this.p1);
    }
}

app/controllers/addObserver1.js

Javascript

import Ember from 'ember';

export default Ember.Controller.extend({
    value: 'value',
    init() {
        this._super(...arguments);
        this.addObserver('value', this, 'Change');
    },

    Change() {
        console.log('value changed');
    },
    actions: {
        remove(data) {
            this.p1.set('[]', this.p1.without(data));
        },
        print() {
            let ans = this.p1.get('[]');
            alert(ans.join('\n'))
        },
    },
});

app/templates/addObserver1.hbs

HTML

<ul>
    <h3>List is : </h3>
      {{#each @model as |party|}}
        <li>{{party}}</li>
      {{/each}}
</ul>
<br />
{{input value=this.value}}
<br />
<input
    type="button"
      id="check-atIndex"
      value="Remove"
      {{action "remove" this.value}}
/>
<br /><br />
<input
    type="button"
      id="print-item"
      value="Print All Items"
      {{action "print" this.value}}
/>

Output:

Ember.js Controller addObserver() Method

Example 2: Type the following code to generate the route for this example:

ember generate route addObserver2

app/controllers/addObserver2.js

Javascript

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

import Ember from 'ember'
let Student = Ember.Object.extend({
    // these will be supplied by `create`
    firstName: null,
    lastName: null,

    fullName: Ember.computed('firstName', 'lastName', function () {
        return `${this.get('firstName')} ${this.get('lastName')}`;
    }),

    Changed: Ember.observer('fullName', function () {
        console.log(`fullName changed to: ${this.get('fullName')}`);
    })
});
export default class Array2Controller extends Controller {

    stu2 = Student.create({
        firstName: 'Kasual',
        lastName: 'Singh',
        Id: 'stu2'
    });
    stu0 = Student.create({
        firstName: 'Yehuda',
        lastName: 'Katz',
        Id: 'stu0'
    });
    stu1 = Student.create({
        firstName: 'Yella',
        lastName: 'melo',
        Id: 'stu1'
    });
    stu3 = Student.create({
        firstName: 'Pokhu',
        lastName: 'Verma',
        Id: 'stu3'
    });
    value = this.stu3.get('Id');
    students = [this.stu0, this.stu1, this.stu2, this.stu3]
    @action
    print(data1, data2) {
        let ans = this.students.findBy('Id', data1)
        ans.set('firstName', data2)
    }
}

app/templates/addObserver2.hbs

HTML

<table>
    <tr>
        <th>Name</th>
        <th>Id</th>
      </tr>
      {{#each this.students as |detail|}}
        <tr>
            <td>{{detail.fullName}}</td>
              <td>{{get detail "Id"}}</td>
        </tr>
      {{/each}}
</table>
<br />
{{input value=this.value}}
{{input value=this.value2}}
<br />
<input
    type="button"
      id="set-code"
      value="Update Student details"
      {{action "print" this.value this.value2}}
/>

Output:

Ember.js Controller addObserver() Method

Reference: https://api.emberjs.com/ember/4.6/classes/Controller/methods/addObserver?anchor=addObserver