add code to pass default branch update test for #44

Author: nelsonic

Diff for: examples/todo-list/todo-app.js

@@ -11,8 +11,14 @@ var initial_model = {
   hash: "#/"
 }
 
-function update(model, action) {     // Update function takes the current state
-  var new_model = JSON.parse(JSON.stringify(model)) // "clone" the model
+/**
+ * `update` transforms the `model` based on the `action`.
+ * @param {String} action - the desired action to perform on the model.
+ * @param {Object} model - the App's data ("state").
+ * @return {Object} updated_model - the transformed model.
+ */
+function update(action, model) {     // Update function takes the current state
+  // var new_model = JSON.parse(JSON.stringify(model)) // "clone" the model
   switch(action) {                   // and an action (String) runs a switch
     // case 'CREATE':
     //   new_model.counters[index] = model.counters[index] + 1;
@@ -23,30 +29,31 @@ function update(model, action) {     // Update function takes the current state
     // case Res: // use ES6 Array.fill to create a new array with values set to 0:
     //   new_model.counters[index] = 0;
     //   break;
-    default: return model; // if action not defined, return curent state.
-  }
-  return new_model;
+    default: // if action unrecognised or undefined,
+      return model; // return model unmodified
+  }   // see: https://softwareengineering.stackexchange.com/a/201786/211301
+  // return new_model;
 }
 
-function view(signal, model, root) {
-  empty(root); // clear root element before re-rendering the App (DOM).
-  model.counters.map(function(counter, index) {
-    return container(index, [                // wrap DOM nodes in an "container"
-      button('+', signal, Inc + '-' + index),    // append index to action
-      div('count', counter),       // create div w/ count as text
-      button('-', signal, Dec + '-' + index),    // decrement counter
-      button('Reset', signal, Res + '-' + index) // reset counter
-    ]);
-  }).forEach(function (el) { root.appendChild(el) }); // forEach is ES5 so IE9+
-}
+// function view(signal, model, root) {
+//   empty(root); // clear root element before re-rendering the App (DOM).
+//   model.counters.map(function(counter, index) {
+//     return container(index, [                // wrap DOM nodes in an "container"
+//       button('+', signal, Inc + '-' + index),    // append index to action
+//       div('count', counter),       // create div w/ count as text
+//       button('-', signal, Dec + '-' + index),    // decrement counter
+//       button('Reset', signal, Res + '-' + index) // reset counter
+//     ]);
+//   }).forEach(function (el) { root.appendChild(el) }); // forEach is ES5 so IE9+
+// }
 
 /* module.exports is needed to run the functions using Node.js for testing! */
 /* istanbul ignore next */
 if (typeof module !== 'undefined' && module.exports) {
   module.exports = {
     model: initial_model,
     update: update,
-    view: view
+    // view: view
   }
 }
 

Diff for: test/todo-app.test.js

@@ -13,3 +13,10 @@ test('todo `model` (Object) has desired keys', function (t) {
   t.true(Array.isArray(app.model.todos), "model.todos is an Array")
   t.end();
 });
+
+test('todo `update` default case should return model unmodified', function (t) {
+  const model = JSON.parse(JSON.stringify(app.model));
+  const unmodified_model = app.update('UNKNOWN_ACTION', model);
+  t.deepEqual(model, unmodified_model, "model returned unmodified");
+  t.end();
+});

Diff for: todo-list.md

@@ -304,7 +304,6 @@ The **`JSDOC`** for our `update` function is:
  * @param {Object} model - the App's data ("state").
  * @return {Object} updated_model - the transformed model.
  */
-
 ```
 
 #### `update` Test
@@ -314,10 +313,63 @@ the function body is a `switch` statement
 that "decides" how to handle a request based on the `action` (_also known as the "message"_).
 
 Given that we _know_ that our `update` function "skeleton"
-(_because this is the "TEA" pattern_)
+will be a `switch` statement
+(_because that is the "TEA" pattern_)
 good test to _start_ with is the `default case`.
 
+Append following test code in `test/todo-app.test.js`:
+
+```js
+test('todo `update` default case should return model unmodified', function (t) {
+  const model = JSON.parse(JSON.stringify(app.model));
+  const unmodified_model = app.update('UNKNOWN_ACTION', model);
+  t.deepEqual(model, unmodified_model, "model returned unmodified");
+  t.end();
+});
+```
+
+If you _run_ this test in your terminal:
+```sh
+node test/todo-app.test.js
+```
+You should see the assertion _fail_:
+![update-default-branch-test-failing](https://user-images.githubusercontent.com/194400/43580847-b78105c0-964e-11e8-81ac-61a1dd8ec535.png)
+
+#### `update` Function Implementation > `switch default case`
+
+Write the _minimum_ code necessary to pass the test.
+
+> Yes, we could just write:
+```js
+function update (action, model) { return model; }
+```
+And that _would_ make the test _pass_. <br />
+But, in light of the fact that we **know** the `update`
+function body will contain a `switch` statement,
+make the test pass by returning the `model` _unmodified_ in the `default` case.
+
+e.g:
+```js
+/**
+ * `update` transforms the `model` based on the `action`.
+ * @param {String} action - the desired action to perform on the model.
+ * @param {Object} model - the App's data ("state").
+ * @return {Object} updated_model - the transformed model.
+ */
+function update(action, model) {     // Update function takes the current state
+  switch (action) {                  // and an action (String) runs a switch
+    default: // if action unrecognised or undefined,
+      return model; // return model unmodified
+  }   // see: https://softwareengineering.stackexchange.com/a/201786/211301
+}
+```
 
+When you re-run the test(s) in your terminal:
+```sh
+node test/todo-app.test.js
+```
+You should see this assertion pass:
+![update-default-branch-test-passing](https://user-images.githubusercontent.com/194400/43581137-c6aa236e-964f-11e8-96d0-ef724659761e.png)
 
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