compare values with the same-value equality algorithm

https://developer.mozilla.org/docs/Web/JavaScript/Equality_comparisons_and_sameness#Same-value_equality

README.md

@@ -4,7 +4,7 @@
 [![Build Status](https://travis-ci.org/shinnn/array-has-duplicates.svg?branch=master)](https://travis-ci.org/shinnn/array-has-duplicates)
 [![Coverage Status](https://img.shields.io/coveralls/shinnn/array-has-duplicates.svg)](https://coveralls.io/github/shinnn/array-has-duplicates)
 
-Check if an [array](http://www.ecma-international.org/ecma-262/5.1/#sec-15.4) includes duplicated values or not
+Check if an `Array` includes duplicated values or not
 
 ```javascript
 arrayHasDuplicates([1, 2, 3, 4, 5]); //=> false
@@ -23,28 +23,31 @@ npm install array-has-duplicates
 
 ### arrayHasDuplicates(*array*)
 
-*array*: `Array`  
-Return: `Boolean`
+*array*: `Array<any>`  
+Return: `boolean`
 
 It returns `true` if the array includes at least one pair of duplicated values, otherwise returns `false`.
 
-*"Duplicated"* means a value is [strictly equal (`===`)][strictequal] to the other value.
-
 ```javascript
 arrayHasDuplicates([3, 3, 3]); //=> true
 arrayHasDuplicates([3, '3', [3]]); //=> false
 ```
 
-Also it ignores all the empty indexes.
+*"Duplicated"* means a value is identical to with another value in the ECMAScript [same-value equality](https://developer.mozilla.org/docs/Web/JavaScript/Equality_comparisons_and_sameness#Same-value_equality) level.
+
+```javascript
+arrayHasDuplicates([0, -0]); //=> false
+```
+
+Note that it ignores all empty indexes.
 
 ```javascript
-arrayHasDuplicates([, , , undefined]); //=> false
+arrayHasDuplicates([, undefined]);
+//=> false, though array[0] and array[1] are both `undefined`
 ```
 
 ## License
 
 Copyright (c) 2016 - 2018 [Shinnosuke Watanabe](https://github.com/shinnn)
 
 Licensed under [the MIT License](./LICENSE).
-
-[strictequal]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Comparison_Operators#Identity_strict_equality_()

index.js

@@ -7,32 +7,36 @@ var appendType = require('append-type');
  * https://github.com/shinnn/array-has-duplicates
 */
 
-function removeEmptyArrayElement() {
-	return true;
+var objectIs = Object.is || function objectIs(x, y) {
+	if (x === y) {
+		return x !== 0 || 1 / x === 1 / y;
+	}
+
+	return x !== x && y !== y; // eslint-disable-line no-self-compare
+};
+
+function is(x) {
+	return objectIs(this, x);
 }
 
-var hasSet = typeof Set === 'function';
+function isAlradyFound(val) {
+	if (this.some(is, val)) {
+		return true;
+	}
+
+	this.push(val);
+
+	return false;
+}
 
 function arrayHasDuplicates(arr) {
 	if (!Array.isArray(arr)) {
 		throw new TypeError('Expected an Array to check if it includes duplicated values, but got ' + appendType(arr) + '.');
 	}
 
-	arr = arr.filter(removeEmptyArrayElement);
-
-	if (arr.length < 300 || !hasSet) {
-		var len = arr.length;
-
-		while (len--) {
-			if (arr.indexOf(arr[len]) !== len) {
-				return true;
-			}
-		}
-
-		return false;
-	}
+	var foundValues = [];
 
-	return arr.length !== 0 && arr.length !== new Set(arr).size;
+	return arr.some(isAlradyFound, foundValues);
 }
 
 module.exports = arrayHasDuplicates;

index.mjs

@@ -4,30 +4,34 @@
 */
 import appendType from 'append-type';
 
-function removeEmptyArrayElement() {
-	return true;
+var objectIs = Object.is || function objectIs(x, y) {
+	if (x === y) {
+		return x !== 0 || 1 / x === 1 / y;
+	}
+
+	return x !== x && y !== y; // eslint-disable-line no-self-compare
+};
+
+function is(x) {
+	return objectIs(this, x);
 }
 
-var hasSet = typeof Set === 'function';
+function isAlradyFound(val) {
+	if (this.some(is, val)) {
+		return true;
+	}
+
+	this.push(val);
+
+	return false;
+}
 
 export default function arrayHasDuplicates(arr) {
 	if (!Array.isArray(arr)) {
 		throw new TypeError('Expected an Array to check if it includes duplicated values, but got ' + appendType(arr) + '.');
 	}
 
-	arr = arr.filter(removeEmptyArrayElement);
-
-	if (arr.length < 300 || !hasSet) {
-		var len = arr.length;
-
-		while (len--) {
-			if (arr.indexOf(arr[len]) !== len) {
-				return true;
-			}
-		}
-
-		return false;
-	}
+	var foundValues = [];
 
-	return arr.length !== 0 && arr.length !== new Set(arr).size;
+	return arr.some(isAlradyFound, foundValues);
 }

package.json

@@ -6,7 +6,6 @@
 	"author": "Shinnosuke Watanabe (https://github.com/shinnn)",
 	"license": "MIT",
 	"scripts": {
-		"bench": "node -p \"require('chalk').yellow('NOTE: Smaller is better.\\n')\" && node benchmark/index-of.js && node benchmark/set.js && node benchmark/main.js",
 		"prebuild": "eslint .",
 		"build": "rollup --config=node:module",
 		"pretest": "npm run-script build",
@@ -23,6 +22,8 @@
 		"duplicate",
 		"duplicates",
 		"duplicated",
+		"same",
+		"same-value-equality",
 		"check",
 		"if"
 	],

test.js

@@ -22,6 +22,12 @@ test('arrayHasDuplicates()', t => {
 		'should compare values with the strict equal operator.'
 	);
 
+	t.equal(
+		arrayHasDuplicates([0, -0]),
+		false,
+		'should differentiate negative zero from positive zero.'
+	);
+
 	t.equal(
 		arrayHasDuplicates([, , , undefined]), // eslint-disable-line no-sparse-arrays
 		false,