React technical challenge @ MUI

This challenge is part of the hiring process for some of the Software Engineer positions at MUI. The idea is to make as much progress as possible under a given time constraint (3-4 hours).

Why are we doing this?

At MUI, because we are a DevTools company, you'll make product decisions. You will flesh out product requirements and turn them into a technical design and implementation. This challenge simulates that, we will review the product decisions you make, the quality of the code, as well as how you approach diving into a complex codebase. We want to get a glimpse of how you will perform in the role.

Context about MUI

MUI's objective is to become the UI toolkit for React developers. We're unifying the fragmented ecosystem of dependencies into a single set of simple, beautiful, consistent, and accessible React components.

Our mission is, ultimately, to make building great UIs and web apps a breeze ⎯ quicker, simpler, and accessible to more people. At the end of the day, it's about writing less code.

Head to our Handbook to learn more.

The challenge

Your challenge is split into two phases:

• In the first phase, your objective is to build a simplified version of a Combo Box.
• In the second phase, your objective is to handle a fake GitHub issue of the same Combo Box component that runs in production.

First phase

~2 hours - The basics

Introduction

A Combo Box is a component that combines a text box with a dropdown list, allowing the users to choose among a long list of mutually exclusive values. For instance, Chrome's URL bar:

Objective

The goal of this first phase is to implement the above component:

• no high-level primitives, e.g. without <datalist>, without pre-made React components
• reproduce as much of the UX of Chrome's URL bar as possible. You can also benchmark with the UX of Google's main search bar to adjust the tradeoffs. The end goal is to be able to use the component for the same search use case.
• use React hooks, no class components
• be written in TypeScript, any and @ts-ignore are accepted but need to be justified (comments)
• be performant, it can render 300 options without virtualization
• be accessible, end-users could only use the keyboard, see WAI-ARIA for guidance. Their examples might be the most helpful.
• looks great, has a beautiful UI
• make the existing test pass, add tests for edge cases
• has no linting errors (yarn prettier && yarn eslint && yarn typescript)
• has an ergonomic API

In practice, such a solution would require dozens of hours to reach the high-quality bar we expect MUI components to have (if not > 100 hours). To keep the challenge short, we will focus on solving a subset of the problem:

• you may drop behaviors that have a too high time opportunity cost. Please document the behaviors you drop and why.
• don't write documentation but enough to see how to use the component, e.g. one demo.
• only one browser support (of your choice)
• no touch screen support
• no dark mode support
• no right-to-left support
• no npm publish

Work environment

To save you time, a working environment was created with Next.js/TypeScript/eslint/prettier/testing-library/Babel, etc. It's a reproduction of the mui/material-ui repository. You can install this environment by following these steps:

• clone the repo: git clone git@github.com:mui/tech-challenge-react.git
• install the dependencies: yarn
• use a Node.js's version >= 18.0.0 and < 21.0.0
• start Next.js: yarn start
• open http://0.0.0.0:3002/components/phase1/

You can find the source of this URL at docs/pages/components/phase1.tsx, it already contains a data set of 248 countries.

You can find the existing test to make pass at docs/pages/components/ComboBox.test.js. The tests in the file can be run with this command: yarn t ComboBox.

Second phase

~1-2 hours - The polish

Introduction

Congratulations, you have completed the first implementation of the component in the first phase. Now, it's time to push it to production!

Fast forward months and hours of iteration on the component, you might reach a state close to the same Combo Box component that we were running in production around January 2021.

This second phase is about handling a fake GitHub issue a developer has just opened.

Issue

Developers rarely spend the time to explain the pain point they face in detail nor provide context. Lucky for us, we received a reproduction we can leverage:

Hi, I'm facing problem, please help.
> #### Steps to reproduce 🕹
> 1. Open https://codesandbox.io/s/recursing-mclean-2dub0?file=/demo.tsx
2. Type 1 in the textbox. Once the options are loaded, the component displays options filtered by input value. The callback onHighlightChange log correct value option 1 1.
3. Then type 2 in the textbox. The textbox now contains 12. The component displays options filtered by input value. The callback onHighlightChange log wrong value option 1 1 instead of option 2 12.
> #### Environment
> @material-ui/core@5.0.0-alpha.15

Guidance

The repository you have cloned in the beginning includes a simplified version of https://github.com/mui/material-ui on v5.0.0-alpha.15.

• The documentation of the Autocomplete component can be found at http://0.0.0.0:3002/components/autocomplete/. It's updating live with changes in the source.
• The tests of the Autocomplete component can be found at packages/material-ui/src/Autocomplete/Autocomplete.test.js
• The tests of the Autocomplete component can be run with yarn t Autocomplete.
• We expect the bug fix to come with a new test that will prevent regressions.
• Fixing this bug might require breaking other tests, you should evaluate if the tradeoff is acceptable.

Objective

The goal of this second phase is to improve the component from v5.0.0-alpha.15 and hopefully solve most of the pain points of this developer.

• Commit your changes in your fork
• Explain the tradeoff taken, compared to the alternatives

Submission

Instructions:

• DO NOT fork / host your project on a public repository.
• Please send us a zip file containing this project using the upload link that we have provided by email (with the .git folder).
• To significantly reduce the size of the archive, remove the /_node_modules_/ and /docs/.next/ folders.
• If you don't have the upload link, you can send it to job@mui.com.

We're excited and looking forward to seeing what you'll create! Good luck 🚀