Difference between constant and value

A constant can be injected anywhere.

A constant can not be intercepted by a decorator, that means that the value of a constant should never be changed.

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;

});

Value differs from constant in that value can not be injected into configurations, but it can be intercepted by decorators.

var app = angular.module('app', []);

app.value('greeting', 'Hello');

app.config(function ($provide) {

    $provide.decorator('greeting', function ($delegate) {

        return $delegate + ' World!';

    });

});

Constant in angular:

A constant can be injected everywhere. A constant can not be intercepted by a decorator, that means that the value of a constant should never be changed (though it is still possible to change it programmatically in Angular 1.x).

Syntax:

.constant(name, value);

name --> name of constant

value --> value of constant

Example:

var myAppangular.module('myApp', []);

myApp.constant("clientId", "123456");

myApp.config(['clientId', function(clientId){

console.log(clientId);

}])

myApp.controller('myController',['clientId', function(clientId){

console.log(clientId);

}])

so, the difference between constant and value is constant inject in  config block but value can't