replace sorter with d3.ascending; update comments; add getTime test

src/lib/lib/calcUniques.js

@@ -10,7 +10,7 @@
 	@param {{x?: Function, y?: Function, z?: Function, r?: Function}} fields An object containing `x`, `y`, `r` or `z` keys that equal an accessor function. If an accessor function returns an array of values, each value will also be evaluated..
 	@returns {{x?: [min: Number, max: Number]|[min: String, max: String], y?: [min: Number, max: Number]|[min: String, max: String], z?: [min: Number, max: Number]|[min: String, max: String], r?: [min: Number, max: Number]|[min: String, max: String]}} An object with the same structure as `fields` but instead of an accessor, each key contains an array of unique items.
 */
-import sorter from '../utils/sorter.js';
+import { ascending } from 'd3-array';
 import getTime from '../utils/getTime.js';
 
 export default function calcUniques (data, fields, { sort = false } = {}) {
@@ -52,7 +52,8 @@ export default function calcUniques (data, fields, { sort = false } = {}) {
 				const vl = val.length;
 				for (k = 0; k < vl; k += 1) {
 					/**
-					 * If val[k] is a date, return its time. Otherwise, return val[k].
+					 * Date objects of the same date are not equivalent in a Set
+					 * If val[k] is a date we turn it into a time value with getTime, otherwise getTime returns val[k].
 					 * Push val[k] to results, though, so that we aren't converting the users data.
 					 */
 					if (!set.has(getTime(val[k]))) {
@@ -62,17 +63,18 @@ export default function calcUniques (data, fields, { sort = false } = {}) {
 				}
 			} else {
 				/**
-				 * If val is a date, return its time. Otherwise, return val.
-				 * Push val to results, though, so that we aren't converting the users data.
+				 * Date objects of the same date are not equivalent in a Set
+				 * If val[k] is a date we turn it into a time value with getTime, otherwise getTime returns val[k].
+				 * Push val[k] to results, though, so that we aren't converting the users data.
 				 */
-				if (!set.has(getTime(val)) ){
+				if (!set.has(getTime(val))) {
 					set.add(getTime(val));
 					results.push(val);
 				}
 			}
 		}
 		if (sort === true) {
-			results.sort(sorter);
+			results.sort(ascending);
 		}
 		uniques[s] = results;
 	}

src/lib/utils/getTime.js

@@ -1,5 +1,7 @@
 /**
  * If val is a date, return its time. Otherwise, return val.
+ * @param {Date|*} val
+ * @returns {number|*}
  */
 export default function getTime (val) {
 	if (Object.prototype.toString.call(val) === '[object Date]') {

test/getTime.test.js

@@ -0,0 +1,27 @@
+/* globals describe it */
+import * as assert from 'assert';
+import fn from '../src/lib/utils/getTime.js';
+
+const name = 'getTime';
+
+const tests = [
+	{ args: [0], expected: 0 },
+	{ args: [[0, 1, 2]], expected: [0, 1, 2] },
+	{ args: ['hello'], expected: 'hello' },
+	{ args: [Infinity], expected: Infinity },
+	{ args: [null], expected: null },
+	{ args: [undefined], expected: undefined },
+	{ args: [new Date(2020, 0, 1)], expected: 1577854800000 },
+	{ args: [new Date(Date.UTC(2020, 0, 1))], expected: 1577836800000 }
+];
+
+describe(name, () => {
+	tests.forEach((test) => {
+		describe(JSON.stringify(test.args), () => {
+			it(`should equal ${JSON.stringify(test.expected)}`, () => {
+				const actual = fn(...test.args);
+				assert.deepStrictEqual(actual, test.expected);
+			});
+		});
+	});
+});