add support for extensions in json1

src/feed.js

@@ -10,6 +10,7 @@ class Feed {
     this.items = []
     this.categories = []
     this.contributors = []
+    this.extensions = []
   }
 
   addItem(item) {
@@ -24,6 +25,10 @@ class Feed {
     this.contributors.push(contributor)
   }
 
+  addExtension(extension) {
+    this.extensions.push(extension)
+  }
+
   render(format) {
     console.warn('DEPRECATED: use atom1() or rss2() instead of render()');
     if (format === 'atom-1.0') {
@@ -377,7 +382,7 @@ class Feed {
   }
 
   json1() {
-    const { options, items } = this
+    const { options, items, extensions } = this
     let feed = {
       version: 'https://jsonfeed.org/version/1',
       title: options.title,
@@ -409,6 +414,11 @@ class Feed {
           feed.author.url = options.author.link;
       }
     }
+
+    extensions.forEach(e => {
+      feed[e.name] = e.objects;
+    });
+
     feed.items = items.map(item => {
       let feedItem = {
         id: item.id,

src/feed.spec.js

@@ -55,6 +55,14 @@ feed.addItem({
   image: 'https://example.com/hello-world.jpg'
 })
 
+feed.addExtension({
+  name: '_example_extension',
+  objects: {
+    about: 'just an extension example',
+    dummy: 'example',
+  }
+});
+
 test('it should generate an RSS 2.0 feed', () => {
   let expected = `<?xml version=\"1.0\" encoding=\"utf-8\"?>
 <rss version=\"2.0\" xmlns:atom=\"http://www.w3.org/2005/Atom\">
@@ -169,6 +177,10 @@ test('it should generate a JSON v1 Feed', () => {
             "title": "Hello World",
             "url": "https://example.com/hello-world"
         }],
+        "_example_extension": {
+          "about": "just an extension example",
+          "dummy": "example"
+        },
         "title": "Feed Title",
         "version": "https://jsonfeed.org/version/1"
     };