AngularJS Service vs Factory vs Provider: Complete Guide

Service, Factory, and Provider are three different ways to create and register services in AngularJS, with each serving different use cases and having distinct implementation patterns. While all three ultimately result in singleton objects that can be injected throughout your application, they differ in their flexibility, configuration capabilities, and implementation approach.

Contents

• Core Differences Between Service, Factory, and Provider
• When to Use a Service
• When to Use a Factory
• When to Use a Provider
• Implementation Examples
• Best Practices

Core Differences Between Service, Factory, and Provider

The fundamental relationship between these three concepts is that Provider is the most primitive and flexible, while Service and Factory are specialized versions of Provider with different syntactic approaches.

Provider

• Most flexible and powerful option
• Can be configured from app.config() using .config()
• Uses a $get() method to define the service logic
• Acts as the base implementation that both service and factory build upon
• According to the official AngularJS documentation, providers are objects with a $get() method that AngularJS calls to create the service

Service

• Simplified version of factory that uses constructor functions
• Uses the this keyword instead of returning an object
• Instantiated with the new keyword internally
• As explained in the Medium article, services follow different rules than factories: they use the keyword this instead of declaring an object, they are instantiated with the new keyword, and they don’t actually return anything

Factory

• Creates an object, adds properties to it, then returns that object
• More flexible in how the object is created and configured
• Can be called like a normal function
• According to Stack Overflow, “If you want your function to be called like a normal function, use factory”

When to Use a Service

Use a Service when:

1. You need a simple object that doesn’t require any configuration - As stated in SourceBae, “You should use a service in AngularJS when you need a simple object that does not require any configuration.”

2. You want to share data across the entire application lifetime - According to LinkedIn, “It is a singleton object. Use it when you need to share a single object across the application. For example, authenticated user details.”

3. You prefer constructor function syntax - When you’re comfortable with this keyword and constructor patterns

4. You need consistent behavior across different controllers - As mentioned in ui.dev, “Services however provide a means for keeping data around for the lifetime of an application while they also can be used across different controllers in a consistent manner.”

When to Use a Factory

Use a Factory when:

1. You need flexibility in how the object is created - Factory allows you to create an object in any way you see fit, as long as you return it.

2. You want to call functions like normal functions - The Stack Overflow answer suggests using factory when “you want your function to be called like a normal function.”

3. You need to return different objects based on conditions - Factory can have conditional logic that returns different objects or configurations.

4. You need to configure the service before instantiation - Unlike services, factories can be more easily configured.

5. You prefer object literal syntax - When you like adding properties to an object and returning it.

When to Use a Provider

Use a Provider when:

1. You need module-wide configuration - As stated in Atmosera, “Use a provider when you want to be able to provide module-wide configuration for your object before making it available.”

2. You need the most flexibility and power - According to Stack Overflow, “Unlike a service which is a simplified version of factory, a provider is a more complex, but more flexible way of initializing the ‘global’ variables, with the biggest flexibility being the option to set values from the app.config.”

3. You need to configure settings from app.config() - This is the only one of the three that can be configured during the configuration phase of AngularJS.

4. You are creating reusable modules - When your service might be used across different applications with different configurations.

5. You need to expose configuration methods - Providers can have methods that can be called during configuration.

Implementation Examples

Service Example

// Service definition
myApp.service('userService', function() {
  this.currentUser = null;
  this.isLoggedIn = false;
  
  this.login = function(username, password) {
    // authentication logic
    this.currentUser = username;
    this.isLoggedIn = true;
  };
  
  this.logout = function() {
    this.currentUser = null;
    this.isLoggedIn = false;
  };
});

// Usage
myApp.controller('myController', function(userService) {
  userService.login('admin', 'password');
  console.log(userService.isLoggedIn); // true
});

Factory Example

// Factory definition
myApp.factory('dataService', function() {
  var service = {};
  
  service.getAllUsers = function() {
    // fetch users from API
    return fetch('/api/users');
  };
  
  service.getUserById = function(id) {
    // fetch specific user
    return fetch('/api/users/' + id);
  };
  
  return service;
});

// Usage
myApp.controller('myController', function(dataService) {
  dataService.getAllUsers().then(function(users) {
    console.log(users);
  });
});

Provider Example

// Provider definition
myApp.provider('apiService', function() {
  var baseUrl = 'https://api.example.com';
  
  this.setBaseUrl = function(url) {
    baseUrl = url;
  };
  
  this.$get = function($http) {
    var service = {};
    
    service.getData = function(endpoint) {
      return $http.get(baseUrl + endpoint);
    };
    
    return service;
  };
});

// Configuration
myApp.config(function(apiServiceProvider) {
  apiServiceProvider.setBaseUrl('https://custom.api.com');
});

// Usage
myApp.controller('myController', function(apiService) {
  apiService.getData('/users').then(function(response) {
    console.log(response.data);
  });
});

Best Practices

General Guidelines

1. Start with Factory - For most cases, factory provides the best balance of flexibility and simplicity.

2. Use Service for constructor-like patterns - When you’re more comfortable with this and constructor functions.

3. Reserve Provider for complex configuration needs - Only use provider when you absolutely need the configuration capabilities.

4. Consider the team’s familiarity - Choose the pattern that your team is most comfortable with.

Performance Considerations

• All three are singletons - Once created, they persist for the lifetime of the application.
• Factory calls happen once - The factory function is called once when the service is first needed.
• Service instantiation happens once - The service constructor is called once with new.
• **Provider’s $get is called once** - The `$get` method is called once when the service is first needed.

Migration Path

If you find your service becoming complex:

1. Service → Factory - When you need more flexibility in object creation
2. Factory → Provider - When you need configuration capabilities
3. You can always use Provider - As Simply Good Code states, “you can accomplish everything you want using just provider.”

Conclusion

The key differences between Service, Factory, and Provider in AngularJS boil down to their flexibility and configuration capabilities. Service is the simplest, using constructor functions with this keyword, ideal for sharing singleton objects across your application. Factory offers more flexibility by allowing you to create and return objects in any way you prefer, making it suitable for when you need conditional logic or different object creation patterns. Provider is the most powerful and flexible, allowing module-wide configuration through app.config(), and should be used when you need to configure your service before it’s available to the rest of your application.

For most development scenarios, start with Factory as it provides the best balance of power and simplicity. Only move to Service if you prefer constructor syntax, or to Provider when you absolutely need the configuration capabilities. Remember that all three ultimately create singleton objects, so your choice should be based on your specific implementation needs rather than performance considerations.

Sources

1. AngularJS: Service vs provider vs factory - Stack Overflow
2. What’s the difference between service, factory and provider in AngularJS? - LinkedIn
3. AngularJS: Factory vs Service vs Provider | Medium
4. AngularJS Factory vs Service vs Provider: Understanding Differences - Atmosera
5. AngularJS: Factory vs Service vs Provider - ui.dev
6. Service vs Factory - Once and for all - thoughtram
7. AngularJS : When to use service instead of factory - Stack Overflow
8. AngularJS: Difference between Service vs Provider vs Factory - Simply Good Code
9. Difference between factory, service & provider ? - GeeksforGeeks
10. AngularJS: Service vs provider vs factory - SourceBae