Mastering Polymorphism and Dependency Injection in AngularJS: Tips and Tricks for Success

Question

Mastering Polymorphism and Dependency Injection in AngularJS: Tips and Tricks for Success

This question revolves around design patterns. Rather than seeking a solution for achieving polymorphism in a service, I am interested in exploring the most widely accepted approach.

Imagine there is a service named getData which retrieves data from various sources such as a database, text file, or hardcoded input. The output is determined by the settings on the $scope within the controller. In this scenario, let's assume that the behavior of getData is influenced by the dataSource variable.

angular.module('testApp').controller('testController'), [$scope, myAwesomeService, function ($scope, myAwesomeService){
    $scope.dataSource = 'database'; //defines the source of the data

    $scope.getData = function() {
        //use myAwesomeService, get the data and output

        if($scope.dataSource ==='database') {
             return //perform operation based on 'database'
        }            

        else if($scope.dataSource ==='text') {
             return //perform operation based on 'text'
        } 

        else if($scope.dataSource ==='csvfile') {
             return //perform operation based on 'csvfile'
        } 
        else if($scope.dataSource ==='form') {
             return //perform operation based on 'form'
        } 

    }

}]);

Questions:

How can polymorphism be generally achieved in Javascript? In JavaScript, achieving polymorphism may not have established best practices. Personally, I typically rely on interfaces by implementing dependency injection and passing objects that conform to the same interface. By calling a shared method from the controller, I maintain flexibility without getting involved in specific implementation details.
How should this be implemented using AngularJS? Is there a standard Angular way of implementing polymorphism? Can you provide a conventional approach to achieving polymorphism in AngularJS?

javascript angularjs oop polymorphism

Answer 1

Answer №1

Initially, I intended to leave a comment, but upon realizing its potential length, I decided to provide an answer instead.

In the realm of ES5, polymorphism and inheritance can be achieved through prototyping methods.

Here is a simple example:

function Auto(name,year){
   this.year=year;
   this.name=name;
}
Auto.prototype.showYear = function(){
   console.log(this.year);
}

function Car(name,year, model){
   Auto.call(this,name,year);
   this.model=model;
}
Car.prototype = Object.create(Auto.prototype);

//example usage
var car = new Car('BMW',2015,'320d');
car.showYear(); // outputs 2015

In the context of ES6, achieving the same can be done using `class` functions. For further details, refer to this insightful guide: HERE (it promises to be enlightening!)

Following is some code that might address your query. Hopefully, it aligns with what you are seeking:

function BaseService(){
    this.dataSource='database';
}
BaseService.prototype.getData = function(){
    console.log('base: get data');
}

function TextService(){
    this.dataSource='text';
}
TextService.prototype  = new BaseService();
TextService.prototype.getData = function(){
    console.log('child text: get data');
}

function CsvService(){
    this.dataSource='csv';
}
CsvService.prototype  = new BaseService();
CsvService.prototype.getData = function(){
    console.log('child csv: get data');
}

function FormService(){
    this.dataSource='form';
}
FormService.prototype  = new BaseService();
FormService.prototype.getData = function(){
    console.log('child form: get data');
}

angular.module('myApp').factory('awesomeService', function(){

    var service={};

    service.getData = function(dataSource){

        var sourceService;

        if(dataSource==='database'){
             sourceService= new BaseService();
        }

        if(dataSource==='text'){
            sourceService=new TextService();
        }

        if(dataSource==='csv'){
           sourceService = new CsvService();
        }

        if(dataSource==='form'){
          sourceService= new FormService();
        }

        return sourceService.getData(); // assuming getData returns a promise
   }

   return service;
});

angular.module('myApp').controller('myController', function($scope,awesomeService){
  var myDataSource='database';

  $scope.getData = function(){
    awesomeService.getData(myDataSource).then(function(data){
         $scope.result=data;
    });
  }
});

Answer 2

Initially, I intended to leave a comment, but upon realizing its potential length, I decided to provide an answer instead.

In the realm of ES5, polymorphism and inheritance can be achieved through prototyping methods.

Here is a simple example:

function Auto(name,year){
   this.year=year;
   this.name=name;
}
Auto.prototype.showYear = function(){
   console.log(this.year);
}

function Car(name,year, model){
   Auto.call(this,name,year);
   this.model=model;
}
Car.prototype = Object.create(Auto.prototype);

//example usage
var car = new Car('BMW',2015,'320d');
car.showYear(); // outputs 2015

In the context of ES6, achieving the same can be done using `class` functions. For further details, refer to this insightful guide: HERE (it promises to be enlightening!)

Following is some code that might address your query. Hopefully, it aligns with what you are seeking:

function BaseService(){
    this.dataSource='database';
}
BaseService.prototype.getData = function(){
    console.log('base: get data');
}

function TextService(){
    this.dataSource='text';
}
TextService.prototype  = new BaseService();
TextService.prototype.getData = function(){
    console.log('child text: get data');
}

function CsvService(){
    this.dataSource='csv';
}
CsvService.prototype  = new BaseService();
CsvService.prototype.getData = function(){
    console.log('child csv: get data');
}

function FormService(){
    this.dataSource='form';
}
FormService.prototype  = new BaseService();
FormService.prototype.getData = function(){
    console.log('child form: get data');
}

angular.module('myApp').factory('awesomeService', function(){

    var service={};

    service.getData = function(dataSource){

        var sourceService;

        if(dataSource==='database'){
             sourceService= new BaseService();
        }

        if(dataSource==='text'){
            sourceService=new TextService();
        }

        if(dataSource==='csv'){
           sourceService = new CsvService();
        }

        if(dataSource==='form'){
          sourceService= new FormService();
        }

        return sourceService.getData(); // assuming getData returns a promise
   }

   return service;
});

angular.module('myApp').controller('myController', function($scope,awesomeService){
  var myDataSource='database';

  $scope.getData = function(){
    awesomeService.getData(myDataSource).then(function(data){
         $scope.result=data;
    });
  }
});

Mastering Polymorphism and Dependency Injection in AngularJS: Tips and Tricks for Success

Answer №1

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