fix: ES6 iterator done flag handling

The iterator was incorrectly setting the done flag after checking hasNext(),
which caused the for...of loop to skip the last value or not iterate at all.

Fixes #397

Author: harrisiirak

src/CronExpression.ts

@@ -575,8 +575,12 @@ export class CronExpression {
   [Symbol.iterator](): Iterator<CronDate> {
     return {
       next: () => {
-        const schedule = this.#findSchedule();
-        return { value: schedule, done: !this.hasNext() };
+        try {
+          const schedule = this.#findSchedule();
+          return { value: schedule, done: false };
+        } catch {
+          return { value: undefined as any, done: true };
+        }
       },
     };
   }

tests/CronExpression.test.ts

@@ -45,11 +45,19 @@ describe('CronExpression', () => {
     expect(prevDate.toISOString()).toBe('2022-01-30T00:00:00.000Z');
   });
 
-  test('should check if there is a next scheduled date', () => {
+  test('should return true if there is a next scheduled date within bounds', () => {
     const cronExpression = new CronExpression(fields, options);
     expect(cronExpression.hasNext()).toBe(true);
   });
 
+  test('should return false if there is no next scheduled date within bounds', () => {
+    const cronExpression = new CronExpression(fields, {
+      ...options,
+      endDate: new Date('2023-01-02T00:00:00Z'),
+    });
+    expect(cronExpression.hasNext()).toBe(false);
+  });
+
   test('should check if there is a previous scheduled date', () => {
     const cronExpression = new CronExpression(fields, options);
     expect(cronExpression.hasPrev()).toBe(true);

tests/CronExpressionParser.test.ts

@@ -243,7 +243,6 @@ describe('CronExpressionParser', () => {
     const options = {
       currentDate: new CronDate('Wed, 26 Dec 2012 14:38:53'),
       endDate: new CronDate('Wed, 26 Dec 2012 15:40:00'),
-      iterator: true,
     };
 
     const interval = CronExpressionParser.parse('*/25 * * * *', options);
@@ -262,9 +261,29 @@ describe('CronExpressionParser', () => {
     val = iterator.next();
     expect(val).not.toBeNull();
     expect(val.value).toBeTruthy();
+    expect(val.done).toBeFalsy();
+
+    val = iterator.next();
+    expect(val).not.toBeNull();
+    expect(val.value).toBeUndefined();
     expect(val.done).toBeTruthy();
   });
 
+  test('valid ES6 iterator works with for..of loop', () => {
+    const options = {
+      currentDate: new CronDate('Wed, 26 Dec 2012 14:38:53'),
+      endDate: new CronDate('Wed, 26 Dec 2012 15:40:00'),
+    };
+    const interval = CronExpressionParser.parse('*/25 * * * *', options);
+
+    const dates = [];
+    for (const date of interval) {
+      dates.push(date);
+    }
+
+    expect(dates.length).toEqual(3);
+  });
+
   test('empty expression', () => {
     const interval = CronExpressionParser.parse('');
     const date = new CronDate();