sum of the first nth term of series

Author: nerdrun

sum_of_the_first_nth_term_of_series/main.js

@@ -0,0 +1,13 @@
+function SeriesSum(n) {
+  /// ES6
+  return [...Array(n).keys()].map((_, idx) => 1 + idx * 3).reduce((acc, val) => (acc += 1 / val, acc), 0).toFixed(2);
+
+  /// for loop
+  let result = 0;
+  for(let i = 0, j = 1; i < n; i++, j+=3) {
+    result += (1 / j);
+  }
+  return result.toFixed(2);
+}
+
+module.exports = SeriesSum;

sum_of_the_first_nth_term_of_series/main.test.js

@@ -0,0 +1,24 @@
+const SeriesSum = require('./main');
+
+/// when the parameter is 0.
+
+describe('When the parameter is 0', () => {
+  test('if 0 returns 0.00 as string', () => {
+    expect(SeriesSum(0)).toBe('0.00');
+  });
+});
+
+describe('Sum series test', () => {
+  test('if 1 returns 1.00 as string', () => {
+    expect(SeriesSum(1)).toBe('1.00');
+  });
+  test('if 2 returns 1.25 as string', () => {
+    expect(SeriesSum(2)).toBe('1.25');
+  });
+  test('if 3 returns 1.39 as string', () => {
+    expect(SeriesSum(3)).toBe('1.39');
+  });
+  test('if 4 returns 1.49 as string', () => {
+    expect(SeriesSum(4)).toBe('1.49');
+  });
+});