Difference Between Constant and Value in AngularJS

Today I was reading AngularJs documentation about Constants and Values.

As far as I understand, I would like to put together all the reading which I gathered.

1. Constant can be used during config phase of Angular Js and Value is can only be used during run phase.

2. A constant can be injected anywhere as its value cannot be changed that is why it cannot be intercepted by a decorator 

For eg:

var app = angular.module('app', []);

app.constant('PI', 3.14159265359);

app.controller('appCtrl', function(PI) {
    var radius = 4;
    // calculate area of the circle
    var area = PI * radius * radius; 
});

A value cannot be injected into configurations, But it can be intercepted by a decorator.

var app = angular.module('app', []);

app.value('greeting', 'Hello');

app.config(function ($provide) {
    $provide.decorator('greeting', function ($delegate) {
        return $delegate + ' World!';
    });
});

You can learn more about decorators in below blog:
http://www.bennadel.com/blog/2870-using-module-decorator-in-angularjs-1-4.htm


3. Objects can be used inside a constant as long as we have not decide to change any value therein.
So, it is best to stick with values if values are changeable.

// Storing multiple constant values inside of an object
// Keep in mind the values in the object mean they can be modified
// Which makes no sense for a constant, use wisely if you do this
var app = angular.module(‘myApp’, []);

app.constant(‘config’, {
    appName: ‘My App’,
    appVersion: 2.0,
    apiUrl: ‘http://www.google.com?api’
});

// Storing multiple values inside of an object
var app = angular.module(‘myApp’, []);

app.value(‘user’, {
    firstName: ’‘,
    lastName: ’‘,
    email: ’’
});