Master the JavaScript interview by practicing 20 carefully curated interview questions and solutions. These problems will provide the tools you need to tackle any question you find in an interview. Allow ~1 hour per question.

Most questions have multiple solutions presented. All solutions are thoroughly explained and time and space complexity are discussed. A passing familiarity with these ideas is expected. You'll learn how to tackle different types of problems so you can proceed with confidence in your interviews.

These questions go beyond the common problems that we've all seen. FizzBuzz and bubble sort? We start past those.

We'll discuss how to refine algorithms. We'll go over clever, advanced ways of manipulating data that interviewers are looking for. You'll walk away more skilled and confident in your problem solving and interviewing abilities.

This course is taught in ES2015.

Master the JavaScript Interview

# Flatten Array

### Instructions

Write a function that will take an array of deeply nested arrays and extract every item, flattening the array. It should return a new array that contains the items of each internal array, preserving order.

**Input**: Array

**Output**: Array

### Examples:

    flatten([ [ [ [1], 2], 3], [4], [], [[5]]]);
    // -> [1, 2, 3, 4, 5]
    
    flatten(['abc', ['def', ['ghi', ['jkl']]]]);
    // -> ['abc', 'def', 'ghi', 'jkl']

### Hints

- As in the last problem, we have to process every item we receive. There's no way to get around that so the best time complexity we can hope for is `O(n)`.

---

# Flatten Array

## Instructions

Write a function that will take an array of deeply nested arrays and extract every item, flattening the array. It should return a new array that contains the items of each internal array, preserving order.

**Input**: Array

**Output**: Array

## Examples:

    flatten([ [ [ [1], 2], 3], [4], [], [[5]]]);
    // -> [1, 2, 3, 4, 5]
    
    flatten(['abc', ['def', ['ghi', ['jkl']]]]);
    // -> ['abc', 'def', 'ghi', 'jkl']

## Hints

- As in the last problem, we have to process every item we receive. There's no way to get around that so the best time complexity we can hope for is `O(n)`.

---

This problem will allow us to perform a task that has practical uses in a developer's career. We'll discuss how to flatten deeply nested arrays and why a recursive solution is a good way to attack this problem.

Introduction

Strings & Arrays

Advanced Strings & Arrays

Algorithms & Data Structures

JavaScript Mastery

Conclusion

Flatten Array

Flatten Array

Instructions

Examples:

Hints