feat(buildFetchUrl): enable optional ids via question mark

README.md

@@ -148,6 +148,7 @@ In an ideal world, your REST API follows all the [right patterns and best practi
 To use the functions that operate on collections, your API and config needs to meet some basic requirements:
 
 * The URL specified on the `fetch` config should return the full collection when the `/:id` is omitted. 
+* URLs can have optional path parameters by including `?`, such as `${process.env.HOST_URL}/users/:userId?/books`.
 * The API must return an array of resource objects. If it returns an object (common in paged APIs), you can use the `transformData` config function to return the array field of the object instead.
 * Each object in the array must have a unique ID field, normally named `id`.  If it is not named `id`, then the field name must be set in the `idKey` prop on the resource config. 
 

__tests__/helpers/url.spec.js

@@ -47,6 +47,29 @@ describe('buildFetchUrl', () => {
     expect(url).toBe('http://api.domain.com/users/123/posts');
   });
 
+  it('should handle empty optional ids by removing extra forward slashes or question marks', () => {
+    const baseUrl = 'http://api.domain.com/users/:userId?/posts/:postId';
+    const url = buildFetchUrl({ url: baseUrl, id: { someId: 'huh' } });
+    expect(url).toBe('http://api.domain.com/users/posts');
+  });
+
+  it('should handle non-empty optional ids', () => {
+    const baseUrl = 'http://api.domain.com/users/:userId?/posts/:postId';
+    const url = buildFetchUrl({ url: baseUrl, id: { userId: '123', someId: 'huh' } });
+    expect(url).toBe('http://api.domain.com/users/123/posts');
+  });
+
+  it('omits `:user?` when id field is not passed', () => {
+    const baseUrl = 'http://api.domain.com/users/:user?/comments';
+    const url = buildFetchUrl({
+      url: baseUrl,
+      opts: {
+        query: { someModifier: 'questionable?' },
+      },
+    });
+    expect(url).toBe('http://api.domain.com/users/comments?someModifier=questionable?');
+  });
+
   it('should add query params', () => {
     const baseUrl = 'http://api.domain.com/users/:userId';
     const url = buildFetchUrl({

src/helpers/url.js

@@ -101,7 +101,7 @@ export function replaceUrlParams({ url, id }) {
 export function buildFetchUrl({ url, id, opts }) {
   const [protocolAndDomain, remainderUrl] = splitUrlByProtocolAndDomain(url);
 
-  let builtUrl = replaceUrlParams({ url: remainderUrl, id });
+  let builtUrl = replaceUrlParams({ url: remainderUrl, id }).replace(/\?\//g, '/');
   builtUrl = addQueryParams({ url: builtUrl, opts });
 
   return protocolAndDomain + builtUrl;