Angularjs Constant and enum with example

As we know the benefit of constant and enum in any other language, we need to it wherever need in our project. But angularjs does not have any enum concept, we will try to create some constants, object to achieve the same goal of enum easily with example. Luckily AngularJS provides a constant service type that can be used for static data that will not change and can be used throughout the application. This can be injected like any other service into any module where it is required.

Let's see the simplest code to declare a constant

var app = angular.module('myApp',[]);
app.constant('Constants', {
    //add all the constants here
}); 

Wherever we need to use this Constants we simply inject and use it, Let add a Roles list of constants

var app = angular.module('myApp',[]);
app.constant('Constants', {
    Roles: {
        admin: 'SYS_ADMIN',
        user: 'SYS_USER',
        guest: 'SYS_GUEST'
    }
}); 

Let's say I want to use this constant into my contact controller then inject 'Constants' and use it like any other object

app.controller('contactCtrl', ['$scope', 'Constants', 
  function ($scope, Constants) {

    $log.log(Constants.Roles['admin']); 

    var role = 'SYS_ADMIN';     
    if(role == Constants.Roles['admin']){
        // Do something
    }
}])

By using this constant service can we create the enum, let's see this with example, suppose we want to create enum of Gender like this in C#

public enum Genter
{
    Male = 1,
    Femate = 2,
    Unknown = 3
}   

The same enum in angular can be created like this:

app.constant('Constants', {
    Roles: { ...},
    Gender: {
        1: 'Male',
        2: 'Female',
        3: 'Unknown'
    }
});

How can we use this Gender enum, It can be used in the same we as we used our Roles constant, see this

var gender = 'Male';
if(gender == Constants.Gender[1]){
    // Do something
}

If you want to use it on view simply put it on the scope $scope.const = Constants; and use it wherever you want in your view

So far it was simple, only the name value or Id value but suppose I have a list of countries with Id, short name and long name an want to access by Id or short name to get the long name then it will be a little bit tricky, let's see what I am talking

app.constant('Constants', {
    Roles: {...},
    Gender: {...},
    Country: [
        { Id: 1, ShortName: 'AR', FullName: 'Argentina' },
        { Id: 2, ShortName: 'CZ', FullName: 'Czech Republic' },
        { Id: 3, ShortName: 'DO', FullName: 'Dominican Republic' },
        { Id: 4, ShortName: 'NZ', FullName: 'New Zealand' },
        { Id: 5, ShortName: 'SA', FullName: 'Saudi Arabia' }
    ]
 });

As you can see the full name have space in some country names, even if we will try to create the enum in C# or any other language, we would need to define the enum name as well as the description.

If want want to use by Id then simply we can use the index be reducing one in the value because index start from zero, which is not the good example but if it can help anyone, like this

var someId = 4;
Constants.Country[someId - 1].ShortName OR
Constants.Country[someId - 1].FullName

But if we want to get the full name by short name then we can use like this:

var shortName = 'NZ';
Constants.Country.filter(function (items) { return items.ShortName === shortName; })[0].FullName

If any value match till then it's good, if not, it will through error, so rest of the code after this line will not execute which we cannot afford in any case.

So what is the better way to use this kind of complicated enum or constant? If you have ever worked on any live project in angularjs, we always have some application level service, right?

We will inject this constant in that service and will create a simple method like find full name by short name or find full name by Id or find short name by id etc.

app.factory('Application', ['Constants', function(Constants){ var service = {};
service.findFullNameById = function(key){ return Constants.Country.filter(function(items) { return items.Id === key; })[0].FullName; };
return service; }]);

Since we already injecting our application service in different controller so no need to inject the Constants any more we can use the application service wherever needed like this

var Id = 2;
if(Application.findFullNameById(Id) == 'Dominican Republic'){
    // Do something
} 

Let us know if you have any challenging structure to use as a constant. There might be some cases where you can get the data from database and use as constant, in that case, better to save those records in local storage as it is and write some useful methods and use them directly form there.

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