feat(range): Add range function (#126)

Author: cfleschhut

src/index.js

@@ -43,6 +43,7 @@ import max from './max'
 import slugify from './slugify'
 import convertToRoman from './convertToRoman'
 import gcd from './gcd'
+import range from './range'
 
 export {
   isOdd,
@@ -90,4 +91,5 @@ export {
   slugify,
   convertToRoman,
   gcd,
+  range,
 }

src/range.js

@@ -0,0 +1,29 @@
+export default range
+
+/**
+ * @module range
+ * @description This method creates an array of numbers (positive and/or
+ * negative) progressing from start up to, but not including, end.
+ *
+ * @param {Number} start - The start of the range
+ * @param {Number} end - The end of the range
+ * @param {Number} step - The value to increment or decrement by
+ * @return {Array} - Returns an array of integers containing an arithmetic
+ * progression
+ * */
+
+function range(start = 0, end, step = 1) {
+  if (end === undefined) {
+    end = start
+    start = 0
+  }
+
+  const length = Math.max(Math.ceil((end - start) / step), 0)
+  const rangeArr = Array(length)
+
+  for (let idx = 0; idx < length; idx++, start += step) {
+    rangeArr[idx] = start
+  }
+
+  return rangeArr
+}

test/flatten.test.js

@@ -21,5 +21,5 @@ test('deep flattens an array of arrays', t => {
   const original = [1, 2, [3, 4, [5, 6], 7], 8]
   const expected = [1, 2, 3, 4, 5, 6, 7, 8]
   const actual = flatten(original)
-  t.same(actual, expected)
+  t.deepEqual(actual, expected)
 })

test/range.test.js

@@ -0,0 +1,32 @@
+import test from 'ava'
+import { range } from '../src'
+
+test('creates an array of numbers from start up to end', t => {
+  const expected = [1, 2, 3, 4]
+  const actual = range(1, 5);
+  t.deepEqual(actual, expected)
+})
+
+test('creates an array of numbers starting from zero given an implicit end', t => {
+  const expected = [0, 1, 2, 3]
+  const actual = range(4);
+  t.deepEqual(actual, expected)
+})
+
+test('creates an array of numbers in given steps', t => {
+  const expected = [0, 5, 10, 15]
+  const actual = range(0, 20, 5);
+  t.deepEqual(actual, expected)
+})
+
+test('creates an array of negative numbers given a negative step', t => {
+  const expected = [0, -1, -2, -3]
+  const actual = range(0, -4, -1);
+  t.deepEqual(actual, expected)
+})
+
+test('creates an empty array with no parameters given', t => {
+  const expected = []
+  const actual = range();
+  t.deepEqual(actual, expected)
+})