Tags and tests

test/filterNonUniqueBy/filterNonUniqueBy.js

@@ -0,0 +1,3 @@
+const filterNonUniqueBy = (arr, fn) =>
+arr.filter((v, i) => arr.every((x, j) => i == j == fn(v, x, i, j)));
+module.exports = filterNonUniqueBy;

test/filterNonUniqueBy/filterNonUniqueBy.test.js

@@ -0,0 +1,32 @@
+const expect = require('expect');
+const filterNonUniqueBy = require('./filterNonUniqueBy.js');
+
+test('filterNonUniqueBy is a Function', () => {
+  expect(filterNonUniqueBy).toBeInstanceOf(Function);
+});
+
+test('filterNonUniqueBy works for properties', () => {
+  expect(filterNonUniqueBy(
+  	[
+  		{ id: 0, value: 'a' },
+  		{ id: 1, value: 'b' },
+  		{ id: 2, value: 'c' },
+  		{ id: 1, value: 'd' },
+  		{ id: 0, value: 'e' },
+  	],
+  	(a, b) => a.id == b.id
+  )).toEqual([ { id: 2, value: 'c' } ]);
+});
+
+test('filterNonUniqueBy works for nested properties', () => {
+  expect(filterNonUniqueBy(
+  	[
+  		{ id: 0, value: 'a', n: {p: 0} },
+  		{ id: 1, value: 'b', n: {p: 1} },
+  		{ id: 2, value: 'c', n: {p: 2} },
+  		{ id: 1, value: 'd', n: {p: 0} },
+  		{ id: 0, value: 'e', n: {p: 1} },
+  	],
+  	(a, b) => a.id == b.id
+  )).toEqual([ { id: 2, value: 'c', n: {p: 2} } ]);
+});