How to access global js variable in angular2 component

Within your component you could reference window to access the global variables like so:

rootVar = window["rootVar"];

or

let rootVar = window["rootVar"];

You need to update the file that bootstraps your application to export a function:

import {bootstrap} from '...';
import {provide} from '...';
import {AppComponent} from '...';

export function main(rootVar) {
  bootstrap(AppComponent, [
    provide('rootVar', { useValue: rootVar })
  ]);
}

Now you can provide the variable from the index.html file this way:

<script>
  var rootVar = '@Url.Action("Index","Home",new { Area = ""}, null)';
  System.import('app/main').then((module) => {
    module.main(rootVar);
  });
</script>

Then you can inject the rootVar into components and services this way:

import { Component, Inject} from '@angular/core';

@Component({
  selector: 'home-comp',
  templateUrl: '../Home/Root'
})
export class HomeComponent {   
  constructor(@Inject('rootVar') rootVar:string ) {  }
}