Angular 8, ng build compile twice and duplicate files

Question

I have started a new project in Angular 8 and when executing ng build angular compiles twice, I would like to know why

package-json:

{
  "name": "portability",
  "version": "0.0.0",
  "scripts": {
    "ng": "ng",
    "start": "ng serve",
    "build": "ng build",
    "test": "ng test",
    "lint": "ng lint",
    "e2e": "ng e2e"
  },
  "private": true,
  "dependencies": {
    "@angular/animations": "^8.1.0",
    "@angular/cdk": "^8.0.2",
    "@angular/cli": "^8.1.0",
    "@angular/common": "~8.1.0",
    "@angular/compiler": "~8.1.0",
    "@angular/core": "~8.1.0",
    "@angular/flex-layout": "^8.0.0-beta.26",
    "@angular/forms": "~8.1.0",
    "@angular/material": "^8.0.2",
    "@angular/platform-browser": "~8.1.0",
    "@angular/platform-browser-dynamic": "~8.1.0",
    "@angular/router": "~8.1.0",
    "@ngx-translate/core": "^11.0.1",
    "core-js": "^2.5.4",
    "hammerjs": "^2.0.8",
    "rxjs": "~6.5.2",
    "tslib": "^1.9.0",
    "zone.js": "~0.9.1"
  },
  "devDependencies": {
    "@angular-devkit/build-angular": "~0.801.0",
    "@angular/compiler-cli": "~8.1.0",
    "@angular/language-service": "~8.1.0",
    "@types/jasmine": "~2.8.8",
    "@types/jasminewd2": "~2.0.3",
    "@types/node": "~8.9.4",
    "codelyzer": "^5.0.1",
    "jasmine-core": "~2.99.1",
    "jasmine-spec-reporter": "~4.2.1",
    "karma": "~4.0.0",
    "karma-chrome-launcher": "~2.2.0",
    "karma-coverage-istanbul-reporter": "~2.0.1",
    "karma-jasmine": "~1.1.2",
    "karma-jasmine-html-reporter": "^0.2.2",
    "protractor": "~5.4.0",
    "ts-node": "~7.0.0",
    "tslint": "~5.11.0",
    "typescript": "~3.4.5"
  }
}

node version: v10.16.0

npm version: 6.10.0

Answer 1

This is a new feature of Angular 8, and it's called Differential Loading.

The two seperate builds you are seeing are for different browser targets - the browser the user uses determines what files angular will serve.

New browsers will get code with modern language features, while older browsers will get stable legacy code.