doc(UrlResolver): inline doc

fixes angular#1732

Author: vicb

modules/angular2/src/services/url_resolver.js

@@ -12,6 +12,26 @@ export class UrlResolver {
     }
   }
 
+  /**
+   * Resolves the `url` given the `baseUrl`.
+   *
+   * ## When the `baseUrl` is null
+   *
+   * `url` is resolved in the context of the current document.
+   * If the document location is 'http://www.foo.com/base' and the `url` is 'path/to/here', the resolved url will be
+   * 'http://www.foo.com/base/path/to/here'
+   *
+   * ## When the `baseUrl` is not null
+   *
+   * - when the `url` is null, the `baseUrl` is returned,
+   * - due to a limitation in the process used to resolve urls (a HTMLLinkElement), `url` must not start with a `/`,
+   * - if `url` is relative ('path/to/here', './path/to/here'), the resolved url is a combination of `baseUrl` and `url`,
+   * - if `url` is absolute (it has a scheme: 'http://', 'https://'), the `url` is returned (ignoring the `baseUrl`)
+   *
+   * @param {string} baseUrl
+   * @param {string} url
+   * @returns {string} the resolved URL
+   */
   resolve(baseUrl: string, url: string): string {
     if (isBlank(baseUrl)) {
       DOM.resolveAndSetHref(UrlResolver.a, url, null);
@@ -21,6 +41,11 @@ export class UrlResolver {
     if (isBlank(url) || url == '') return baseUrl;
 
     if (url[0] == '/') {
+      // The `HTMLLinkElement` does not allow resolving this case (the `url` would be interpreted as relative):
+      // - `baseUrl` = 'http://www.foo.com/base'
+      // - `url` = '/absolute/path/to/here'
+      // - the result would be 'http://www.foo.com/base/absolute/path/to/here' while 'http://www.foo.com/absolute/path/to/here'
+      // is expected (without the 'base' segment).
       throw new BaseException(`Could not resolve the url ${url} from ${baseUrl}`);
     }