feat: add range function (silvermine#42)

src/index.ts

@@ -35,3 +35,4 @@ export * from './utils/get';
 export * from './utils/escape-html';
 export * from './utils/make-template';
 export * from './utils/uniq';
+export * from './utils/range';

src/utils/range.ts

@@ -0,0 +1,26 @@
+/**
+ * Creates an array of numbers (positive and/or negative) progressing from 
+ * start up to, but not including, end. A step of -1 is used if a negative start 
+ * is specified without an end or step. If end is not specified, it's set to 
+ * start with start then set to 0.
+ */
+export const range = (start: number, end?: number, step?: number): number[] => {
+   if (end === undefined) {
+      end = start
+      start = 0
+   }
+   step = step ?? (start < end ? 1 : -1)
+
+   if (step === 0) {
+      const length = Math.max(end - start, 0)
+      return Array(length).fill(start)
+   }
+
+   const length = Math.max(Math.ceil((end - start) / step), 0),
+         result = Array(length)
+
+   for (let i = 0; i < length; i++) {
+      result[i] = start + (i * step)
+   }
+   return result
+}

tests/utils/range.test.ts

@@ -0,0 +1,41 @@
+import { expect } from 'chai';
+import {range} from '../../src';
+
+
+describe('range', () => {
+   it('works when only start is provided', () => {
+      expect(range(4)).to.eql([0, 1, 2, 3])
+   }) 
+
+   it('works when only start and end are provided', () => {
+      expect(range(1, 5)).to.eql([1, 2, 3, 4])
+   })
+
+   it('works when start, end, and step is provided', () => {
+      expect(range(0, 20, 5)).to.eql([0, 5, 10, 15])
+   })
+
+   it('works when start is set to a negative number', () => [
+      expect(range(-4)).to.eql([0, -1, -2, -3])
+   ])
+
+   it('fills array with start value if step is zero', () => {
+      expect(range(1, 4, 0)).to.eql([1, 1, 1])
+   })
+
+   it('works when step is a negative number ', () => {
+      expect(range(2, -4, -2)).to.eql([2, 0, -2])
+   })
+
+   it('return an empty array when end and start are the same', () => {
+      expect(range(0, 0)).to.eql([])
+   })
+
+   it('returns an empty array if only start is provided and equals zero', () => {
+      expect(range(0)).to.eql([])
+   })
+
+   it('returns an empty array if arguments do not work', () => {
+      expect(range(5, 1, 2)).to.eql([])
+   })
+})