Replacing Services with TypeScript Classes

Early Angular 1 applications predate the widespread use of module loaders. The strategy of this era was to concatenate source files and rely on Angular 1's dependency injection as a poor-man's module loader. Often services were used to house libraries instead of stateful services.

During conversion, we will introduce Webpack as a module loader. For services that lack state and don't heavily rely on other dependency injected services, we recommend rewriting them using TypeScript modules. The advantages of writing code this way are:

• It becomes framework agnostic (doesn't rely on Angular 1 explicitly)
• It is easier to test
• It instantly works with both Angular 1 and Angular 2

Even services that depend on a limited set of Angular 1 services (e.g. $http) can be rewritten by depending on other libraries (e.g. window.fetch).

How do we get there?

• Convert services using .factory to .service
  • Angular 2's @Injectable expects an object it can use new with, similar to how .service works (e.g. new CalculatorService())
• Replace constructor functions with TypeScript class
• Use the class directly by exporting it.

Example

.factory original

angular.module('calcapp', [])
  .factory('CalculatorService', function () {
    return {
      square: function (a) {
        return a*a;
      },
      cube: function (a) {
        return a*a*a;
      }
    };
  });

Conversion to .service

angular.module('calcapp', [])
  .service('CalculatorService', function () {
    this.square = function (a) {
      return a*a;
    };

    this.cube = function (a) {
      return a*a*a;
    }
  });

Conversion to TypeScript class

class CalculatorService {
  square (a) {
    return a*a;
  }

  cube (a) {
    return a*a*a;
  }
}

angular.module('calcapp', [])
  .service('CalculatorService', CalculatorService);

Skip the middleman

export class CalculatorService { ... }

// elsewhere
import {CalculatorService} from './calculator.service';