# brunnock's solution

## to Flatten Array in the JavaScript Track

Published at Aug 19 2018 · 0 comments
Instructions
Test suite
Solution

#### Note:

This exercise has changed since this solution was written.

Take a nested list and return a single flattened list with all values except nil/null.

The challenge is to write a function that accepts an arbitrarily-deep nested list-like structure and returns a flattened structure without any nil/null values.

For Example

input: [1,[2,3,null,4],[null],5]

output: [1,2,3,4,5]

## Setup

Go through the setup instructions for JavaScript to install the necessary dependencies:

http://exercism.io/languages/javascript/installation

## Running the test suite

The provided test suite uses Jasmine. You can install it by opening a terminal window and running the following command:

``````npm install -g jasmine
``````

Run the test suite from the exercise directory with:

``````jasmine flatten-array.spec.js
``````

In many test suites all but the first test have been marked "pending". Once you get a test passing, activate the next one by changing `xit` to `it`.

## Source

Interview Question https://reference.wolfram.com/language/ref/Flatten.html

## Submitting Incomplete Solutions

It's possible to submit an incomplete solution so you can see how others have completed the exercise.

### flatten-array.spec.js

``````var Flattener = require('./flatten-array.js');

describe('FlattenArray', function () {
var flattener = new Flattener();
it('flattens a nested list', function () {
expect(flattener.flatten([[]])).toEqual([]);
});
xit('flattens a 2 level nested list', function () {
expect(flattener.flatten([1, [2, 3, 4], 5])).toEqual([1, 2, 3, 4, 5]);
});
xit('flattens a  3 level nested list', function () {
expect(flattener.flatten([1, [2, 3, 4], 5, [6, [7, 8]]])).toEqual([1, 2, 3, 4, 5, 6, 7, 8]);
});
xit('flattens a 5 level nested list', function () {
expect(flattener.flatten([0, 2, [[2, 3], 8, 100, 4, [[[50]]]], -2])).toEqual([0, 2, 2, 3, 8, 100, 4, 50, -2]);
});
xit('flattens a 6 level nest list', function () {
expect(flattener.flatten([1, [2, [[3]], [4, [[5]]], 6, 7], 8])).toEqual([1, 2, 3, 4, 5, 6, 7, 8]);
});
xit('flattens a 6 level nest list with null values', function () {
expect(flattener.flatten([0, 2, [[2, 3], 8, [[100]], null, [[null]]], -2])).toEqual([0, 2, 2, 3, 8, 100, -2]);
});
xit('returns an empty list if all values in nested list are null', function () {
expect(flattener.flatten([null, [[[null]]], null, null, [[null, null], null], null])).toEqual([]);
});
});``````
``````class Flattener {
flatten(list,flatList=[]) {
if (Array.isArray(list)) {
list.forEach(x => this.flatten(x,flatList))
} else if (list !== null) {
flatList.push(list);
}
return(flatList);
}
}

module.exports=Flattener;``````