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 +1,24 @@
+/**
+ * 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 function range(start: number, end?: number, step?: number): number[] {
+   if (end === undefined) {
+      end = start;
+      start = 0;
+   }
+
+   if (!step) {
+      step = start < end ? 1 : -1;
+   }
+
+   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('works when step is set to zero', () => {
+      expect(range(1, 4, 0)).to.eql([ 1, 2, 3 ]);
+   });
+
+   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([]);
+   });
+
+});