add filterFalsy snippet, tags, and tests

snippets/filterFalsy.md

@@ -0,0 +1,13 @@
+### filterFalsy
+
+Filters out the falsy values in an array.
+
+Use `Array.prototype.filter()` to get an array containing only truthy values.
+
+```js
+const filterFalsy = arr => arr.filter(Boolean)
+```
+
+```js
+filterFalsy(['', true, {}, false, 'sample', 1, 0]); // [true, {}, 'sample', 1]
+```

tag_database

@@ -75,6 +75,7 @@ everyNth:array,beginner
 extendHex:utility,string,intermediate
 factorial:math,recursion,beginner
 fibonacci:math,array,beginner
+filterFalsy:array,beginner
 filterNonUnique:array,beginner
 filterNonUniqueBy:array,function,intermediate
 findKey:object,function,intermediate

test/filterFalsy.test.js

@@ -0,0 +1,18 @@
+const expect = require('expect');
+const {filterFalsy} = require('._30s.js');
+
+test('filterFalsy is a Function', () => {
+  expect(filterFalsy).toBeInstanceOf(Function);
+});
+
+test('filterFalsy filters different types of falsy values', () => {
+  expect(filterFalsy(['', true, {}, false, 'sample', 1, 0])).toEqual([true, {}, 'sample', 1]);
+});
+
+test('filterFalsy returns an empty array if you pass it an array of falsy values', () => {
+  expect(filterFalsy(['', 0, false, '', false, 0])).toEqual([]);
+});
+
+test('filterFalsy returns all of the truthy elements in an array', () => {
+  expect(filterFalsy([true, null, 'test', {}, []])).toEqual([true, 'test', {}, []]);
+});