Peter Doering

Angular 8 introduced the new ECMAScript standard ES2015. ES2015 is more efficient. Older browsers like IE 11 does support only the previously used ES5. To still have support for IE 9-11 Angular has new feature called Differential Loading. In short it is serving the Angular App in two versions: a ES5 version and ES2015 version. So each browser can decide which version to use.

Unfortunately if your using the Angular Develpment Server ng serve, it will use only ES2015. The reason is, that it would be too slow to compile it always twice for ES2015 and ES5.

There’s a trick how to run ng serve with ES5.

In the file browserslist remove the “not” before “IE 9-11”.

> 0.5%
last 2 versions
Firefox ESR
not dead
IE 9-11

Beside your tsconfig.json add a file tsconfig-es5.json with content:

{
    "extends": "./tsconfig.json",
    "compilerOptions": {
        "target": "es5"
    }
}

Add a new configuration “es5” in the “configurations” and “serve” sections of your angular.json:

{
  ...
  "projects": {
    "my-app": {
      ...
      "configurations": {
        ...
        "es5": {
          "tsConfig": "./tsconfig-es5.json"
        }
      }
    },
    "serve": {
      ...
      "configurations": {
        "production": {
          "browserTarget": "my-app:build:production"
        },
        "es5": {
          "browserTarget": "my-app:build:es5"
        }
      }
    }
    ...
  }
}

Optionally you can add a script to package.json:

"scripts": {
  "start": "ng serve",
  "ie": "ng serve -c es5",
}

Now you can run your Angular App with IE support using:

npm run ie