fix(router): improve error for missing base href

Closes angular#3096

Author: btford

modules/angular2/src/router/location.ts

@@ -1,6 +1,7 @@
 import {LocationStrategy} from './location_strategy';
 import {StringWrapper, isPresent, CONST_EXPR} from 'angular2/src/facade/lang';
 import {EventEmitter, ObservableWrapper} from 'angular2/src/facade/async';
+import {BaseException, isBlank} from 'angular2/src/facade/lang';
 import {OpaqueToken, Injectable, Optional, Inject} from 'angular2/di';
 
 export const appBaseHrefToken: OpaqueToken = CONST_EXPR(new OpaqueToken('locationHrefToken'));
@@ -22,8 +23,14 @@ export class Location {
 
   constructor(public _platformStrategy: LocationStrategy,
               @Optional() @Inject(appBaseHrefToken) href?: string) {
-    this._baseHref = stripTrailingSlash(
-        stripIndexHtml(isPresent(href) ? href : this._platformStrategy.getBaseHref()));
+    var browserBaseHref = isPresent(href) ? href : this._platformStrategy.getBaseHref();
+
+    if (isBlank(browserBaseHref)) {
+      throw new BaseException(
+          `No base href set. Either provide a binding to "appBaseHrefToken" or add a base element.`);
+    }
+
+    this._baseHref = stripTrailingSlash(stripIndexHtml(browserBaseHref));
     this._platformStrategy.onPopState((_) => this._onPopState(_));
   }
 

modules/angular2/test/router/location_spec.ts

@@ -75,5 +75,13 @@ export function main() {
       location.go('user/btford');
       expect(locationStrategy.path()).toEqual('/my/custom/href/user/btford');
     });
+
+    it('should throw when no base href is provided', () => {
+      var locationStrategy = new MockLocationStrategy();
+      locationStrategy.internalBaseHref = null;
+      expect(() => new Location(locationStrategy))
+          .toThrowError(
+              `No base href set. Either provide a binding to "appBaseHrefToken" or add a base element.`);
+    });
   });
 }