fix: add better checking against undefined

The first pass at checking explicitly for `undefined`, rather than just
a falsy value, was not enough. This adds a better test case and fixes
a number of issues I found while getting it to pass.

Closes #112

addon/-private/state-machine/-base.ts

@@ -1,9 +1,9 @@
 import EmberObject, { set } from '@ember/object';
 import MutableArray from '@ember/array/mutable';
-import { isBlank, isPresent } from '@ember/utils';
 import { A } from '@ember/array';
 import { readOnly } from '@ember-decorators/object/computed';
 import { assert } from '@ember/debug';
+import { isNone } from '@ember/utils';
 
 import { StepName } from '../types';
 import StepNode from '../step-node';
@@ -28,7 +28,7 @@ export default abstract class BaseStateMachine extends EmberObject {
   constructor(initialStepName?: StepName) {
     super();
 
-    if (isPresent(initialStepName)) {
+    if (!isNone(initialStepName)) {
       set(this, 'currentStep', initialStepName!);
     }
   }
@@ -37,7 +37,7 @@ export default abstract class BaseStateMachine extends EmberObject {
     const node = new StepNode(this, name, context);
     this.stepTransitions.pushObject(node);
 
-    if (isBlank(this.currentStep)) {
+    if (typeof this.currentStep === 'undefined') {
       set(this, 'currentStep', name);
     }
   }
@@ -67,7 +67,7 @@ export default abstract class BaseStateMachine extends EmberObject {
   activate(step: StepNode | StepName) {
     const name = step instanceof StepNode ? step.name : step;
 
-    assert('No step name was provided', isPresent(step));
+    assert('No step name was provided', !isNone(step));
     assert(
       `"${name}" does not match an existing step`,
       this.stepTransitions.map(node => node.name).includes(name)

addon/components/step-manager.ts

@@ -1,8 +1,8 @@
 import Component from '@ember/component';
 // @ts-ignore: Ignore import of compiled template
 import layout from '../templates/components/step-manager';
-import { get, set } from '@ember/object';
-import { isEmpty, isPresent } from '@ember/utils';
+import { get, getProperties, set } from '@ember/object';
+import { isPresent, isNone } from '@ember/utils';
 import { schedule } from '@ember/runloop';
 import { assert } from '@ember/debug';
 import { action, computed } from '@ember-decorators/object';
@@ -77,7 +77,13 @@ export default class StepManagerComponent extends Component {
   constructor() {
     super(...arguments);
 
-    const initialStep = get(this, 'initialStep') || get(this, 'currentStep');
+    const { initialStep, currentStep } = getProperties(
+      this,
+      'initialStep',
+      'currentStep'
+    );
+
+    const startingStep = isNone(initialStep) ? currentStep : initialStep;
 
     if (!isPresent(this.linear)) {
       this.linear = true;
@@ -87,17 +93,17 @@ export default class StepManagerComponent extends Component {
       ? LinearStateMachine
       : CircularStateMachine;
 
-    set(this, 'transitions', new StateMachine(initialStep));
+    set(this, 'transitions', new StateMachine(startingStep));
   }
 
   @computed('transitions.{currentStep,length}')
   get hasNextStep() {
-    return isPresent(this.transitions.pickNext());
+    return !isNone(this.transitions.pickNext());
   }
 
   @computed('transitions.{currentStep,length}')
   get hasPreviousStep() {
-    return isPresent(this.transitions.pickPrevious());
+    return !isNone(this.transitions.pickPrevious());
   }
 
   didUpdateAttrs() {
@@ -146,7 +152,7 @@ export default class StepManagerComponent extends Component {
 
     // If `currentStep` is present, it's probably something the user wants
     // two-way-bound with the new value
-    if (!isEmpty(this.currentStep)) {
+    if (!isNone(this.currentStep)) {
       set(this, 'currentStep', destination);
     }
 
@@ -157,7 +163,7 @@ export default class StepManagerComponent extends Component {
   transitionToNext() {
     const to = this.transitions.pickNext();
 
-    assert('There is no next step', !!to);
+    assert('There is no next step', !isNone(to));
 
     this.transitionTo(to!);
   }
@@ -166,7 +172,7 @@ export default class StepManagerComponent extends Component {
   transitionToPrevious() {
     const to = this.transitions.pickPrevious();
 
-    assert('There is no previous step', !!to);
+    assert('There is no previous step', !isNone(to));
 
     this.transitionTo(to!);
   }

addon/components/step-manager/step.ts

@@ -2,7 +2,7 @@ import Component from '@ember/component';
 // @ts-ignore: Ignore import of compiled template
 import layout from '../../templates/components/step-manager/step';
 import { get, set } from '@ember/object';
-import { isEmpty, isPresent } from '@ember/utils';
+import { isPresent } from '@ember/utils';
 import { assert } from '@ember/debug';
 import { computed } from '@ember-decorators/object';
 import { tagName } from '@ember-decorators/component';
@@ -33,9 +33,10 @@ export default class StepComponent extends Component {
     super(...arguments);
 
     const nameAttribute = get(this, 'name');
-    const name = isEmpty(nameAttribute)
-      ? Symbol('generated step name')
-      : nameAttribute;
+    const name =
+      typeof nameAttribute === 'undefined'
+        ? Symbol('generated step name')
+        : nameAttribute;
 
     assert('Step name cannot be a boolean', typeof name !== 'boolean');
     assert('Step name cannot be an object', typeof name !== 'object');

tests/integration/step-manager-test.js

@@ -840,4 +840,44 @@ module('step-manager', function(hooks) {
         .exists('The initial step is still visible');
     });
   });
+
+  module('edge cases', function() {
+    test('it handles steps with falsy names', async function(assert) {
+      await render(hbs`
+        {{#step-manager initialStep='' as |w|}}
+          {{#w.step name=''}}
+            <div data-test-empty-string></div>
+          {{/w.step}}
+
+          {{#w.step name=0}}
+            <div data-test-zero></div>
+          {{/w.step}}
+
+          <button {{action w.transition-to-previous}} data-test-previous>
+            Previous step
+          </button>
+
+          <button {{action w.transition-to-next}} data-test-next>
+            Next step
+          </button>
+        {{/step-manager}}
+      `);
+
+      assert
+        .dom('[data-test-empty-string]')
+        .exists('Can start on a step with a falsy name');
+
+      await click('[data-test-next]');
+
+      assert
+        .dom('[data-test-zero]')
+        .exists('Can transition to a next step with a falsy name');
+
+      await click('[data-test-previous]');
+
+      assert
+        .dom('[data-test-empty-string]')
+        .exists('Can transition to a previous step with a falsy name');
+    });
+  });
 });