Merge pull request #68 from jekku/reduce-immutable

Adds immutable solution using Array.reduce

Author: nickjj

javascript/reduce-immutable.js

@@ -0,0 +1,51 @@
+const sections = [
+  {
+    title: 'Getting started',
+    reset_lesson_position: false,
+    lessons: [{ name: 'Welcome' }, { name: 'Installation' }],
+  },
+  {
+    title: 'Basic operator',
+    reset_lesson_position: false,
+    lessons: [
+      { name: 'Addition / Subtraction' },
+      { name: 'Multiplication / Division' },
+    ],
+  },
+  {
+    title: 'Advanced topics',
+    reset_lesson_position: true,
+    lessons: [{ name: 'Mutability' }, { name: 'Immutability' }],
+  },
+]
+
+const lessonReducer = (({lessonCounter, result}, lesson) => {
+  const updatedLesson = {
+    position: lessonCounter + 1,
+    ...lesson
+  }
+  return {lessonCounter: lessonCounter + 1, result: [...result, updatedLesson]}
+})
+
+const sectionReducer = ({lessonCounter, result}, section, index) => {
+  const { reset_lesson_position, lessons } = section
+  const nextLessonCounter = reset_lesson_position ? 0 : lessonCounter
+  const updatedLessons = lessons.reduce(
+    lessonReducer,
+    {lessonCounter: nextLessonCounter, result: []}
+  )
+  const updatedSection = {
+    ...section,
+    lessons: updatedLessons.result,
+    position: index + 1
+  }
+
+  return {
+    result: [...result, updatedSection],
+    lessonCounter: updatedLessons.lessonCounter
+  }
+}
+
+const { result } = sections.reduce(sectionReducer, {lessonCounter: 0, result: []})
+
+console.log(JSON.stringify(result, null, 2))