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Event Emitter

Explore how to use Angular's EventEmitter to emit login and logout events in AuthService. Learn to update the navigation bar dynamically by subscribing to these events in NavbarComponent, and understand how to test these behaviors using Cypress. This lesson helps you manage user authentication state updates and navigation control in Angular applications.

We'll cover the following...

An Event Emitter allows us to emit custom events within our application. We can emit to components such as NavbarComponent whenever a user has been logged in so that it can make event updates as needed, such as updating its template.

The login method in AuthService is one place where we’ll be emitting such an event, because it’s based on whether a user is logged in.

Below is our updated code. Use this to make further changes.

{
  "$schema": "./node_modules/@angular/cli/lib/config/schema.json",
  "version": 1,
  "newProjectRoot": "projects",
  "projects": {
    "lets-get-lunch": {
      "projectType": "application",
      "schematics": {},
      "root": "",
      "sourceRoot": "src",
      "prefix": "app",
      "architect": {
        "build": {
          "builder": "@angular-devkit/build-angular:browser",
          "options": {
            "outputPath": "dist/lets-get-lunch",
            "index": "src/index.html",
            "main": "src/main.ts",
            "polyfills": "src/polyfills.ts",
            "tsConfig": "tsconfig.app.json",
            "aot": true,
            "assets": [
              "src/favicon.ico",
              "src/assets"
            ],
            "styles": [
              "node_modules/bootstrap/dist/css/bootstrap.min.css",
              "src/styles.css"
            ],
            "scripts": [
              "node_modules/jquery/dist/jquery.min.js",
              "node_modules/bootstrap/dist/js/bootstrap.min.js"
            ]
          },
          "configurations": {
            "production": {
              "fileReplacements": [
                {
                  "replace": "src/environments/environment.ts",
                  "with": "src/environments/environment.prod.ts"
                }
              ],
              "optimization": true,
              "outputHashing": "all",
              "sourceMap": false,
              "extractCss": true,
              "namedChunks": false,
              "extractLicenses": true,
              "vendorChunk": false,
              "buildOptimizer": true,
              "budgets": [
                {
                  "type": "initial",
                  "maximumWarning": "2mb",
                  "maximumError": "5mb"
                },
                {
                  "type": "anyComponentStyle",
                  "maximumWarning": "6kb",
                  "maximumError": "10kb"
                }
              ]
            }
          }
        },
        "serve": {
          "builder": "@angular-devkit/build-angular:dev-server",
          "options": {
            "browserTarget": "lets-get-lunch:build"
          },
          "configurations": {
            "production": {
              "browserTarget": "lets-get-lunch:build:production"
            }
          }
        },
        "extract-i18n": {
          "builder": "@angular-devkit/build-angular:extract-i18n",
          "options": {
            "browserTarget": "lets-get-lunch:build"
          }
        },
        "test": {
          "builder": "@angular-devkit/build-angular:karma",
          "options": {
            "main": "src/test.ts",
            "polyfills": "src/polyfills.ts",
            "tsConfig": "tsconfig.spec.json",
            "karmaConfig": "karma.conf.js",
            "assets": [
              "src/favicon.ico",
              "src/assets"
            ],
            "styles": [
              "node_modules/bootstrap/dist/css/bootstrap.min.css",
              "src/styles.css"
            ],
            "scripts": [
              "node_modules/jquery/dist/jquery.min.js",
"node_modules/bootstrap/dist/js/bootstrap.min.js"
            ]
          }
        },
        "lint": {
          "builder": "@angular-devkit/build-angular:tslint",
          "options": {
            "tsConfig": [
              "tsconfig.app.json",
              "tsconfig.spec.json",
              "e2e/tsconfig.json"
            ],
            "exclude": [
              "**/node_modules/**"
            ]
          }
        },
        "e2e": {
          "builder": "@angular-devkit/build-angular:protractor",
          "options": {
            "protractorConfig": "e2e/protractor.conf.js",
            "devServerTarget": "lets-get-lunch:serve"
          },
          "configurations": {
            "production": {
              "devServerTarget": "lets-get-lunch:serve:production"
            }
          }
        }
      }
    }
  },
  "defaultProject": "lets-get-lunch"
}
Updated application code with navbar component

Add Event Emitter to login

First, update our test for login as follows:

  1. Add a spy on the loggedIn property of authService, which has an emit method.
  2. Add an expectation that this method will be called within our login service.
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