Fix: Prevent navigation on empty collections (#607)

README.md

@@ -176,6 +176,12 @@ Additional Methods
 
 `preview.getCurrentCollection()` returns the current collection if any.
 
+`preview.navigateLeft()` shows previous file in the collection.
+
+`preview.navigateRight()` shows next file in the collection.
+
+`preview.navigateToIndex(index)` shows the specified index in the current collection.
+
 `preview.getCurrentFile()` returns the current file being previewed if any. The file object structure is the same as returned by the [Box API](https://developer.box.com/reference#files).
 
 `preview.getCurrentViewer()` returns the current viewer instance. May be undefined if the viewer isn't ready yet and waiting on conversion to happen.

src/lib/Preview.js

@@ -1356,11 +1356,15 @@ class Preview extends EventEmitter {
     /**
      * Shows a preview of a file at the specified index in the current collection.
      *
-     * @private
+     * @public
      * @param {number} index - Index of file to preview
      * @return {void}
      */
     navigateToIndex(index) {
+        if (!Array.isArray(this.collection) || this.collection.length < 2) {
+            return;
+        }
+
         const fileId = this.collection[index];
         this.emit('navigate', fileId);
         this.count.navigation += 1;
@@ -1370,7 +1374,7 @@ class Preview extends EventEmitter {
     /**
      * Shows a preview of the previous file.
      *
-     * @private
+     * @public
      * @return {void}
      */
     navigateLeft() {
@@ -1384,7 +1388,7 @@ class Preview extends EventEmitter {
     /**
      * Shows a preview of the next file.
      *
-     * @private
+     * @public
      * @return {void}
      */
     navigateRight() {

src/lib/__tests__/Preview-test.js

@@ -2076,9 +2076,19 @@ describe('lib/Preview', () => {
                 navigation: 0
             };
 
-            preview.collection = {
-                2: 'file'
-            };
+            preview.collection = [
+                'file', 'file2', 'file3'
+            ]
+        });
+
+        it('should do nothing if the collection is invalid', () => {
+            preview.collection = 'foo'
+            preview.navigateToIndex(1);
+            expect(stubs.emit).to.not.be.called;
+
+            preview.collection = []
+            preview.navigateToIndex(1);
+            expect(stubs.emit).to.not.be.called;
         });
 
         it('should emit the navigation event', () => {
@@ -2093,7 +2103,7 @@ describe('lib/Preview', () => {
 
         it('should load the requested file', () => {
             preview.navigateToIndex(2);
-            expect(stubs.load).to.be.calledWith('file');
+            expect(stubs.load).to.be.calledWith('file3');
         });
     });