Neighborhoods Software Engineer Interview Guide

The 60-second brief

A Software Engineer at Neighborhoods plays a vital role in building and scaling the digital infrastructure that connects local communities. The engineering team is responsible for developing highly responsive, user-centric applications that facilitate real-time interactions, localized content delivery, and seamless user experiences. Because the platform relies on high engagement and localized data, engineers here tackle unique challenges in frontend performance, backend data isolation, and system reliability. In this role, your work directly impacts how users interact with their physical and digital communities. You will be tasked with translating complex product requirements into clean, maintainable code while ensuring the platform remains highly available and performant.

This guide is scoped to a Software Engineer candidate at Neighborhoods.

Focus areas

• JavaScript
• React
• Frontend Development

The Neighborhoods interview process

Neighborhoods candidates report 3 rounds over 3-5 weeks. The stages below are what candidates describe, not a published process.

Recruiter Screen

Initial conversation to align on your background, technical familiarity, and salary expectations.

What to demonstrate

• Initial conversation to align on your background, technical familiarity, and salary expectations
• Depth in JavaScript

How to prepare

• Be able to walk your CV end to end in two minutes, and say why this company specifically.
• Have your salary expectations, notice period and location constraints ready, and ask for the rest of the loop in writing.

Technical Phone Screen

Phone interview led by the VP of Engineering or a lead engineer focusing on past experience and core technical concepts.

What to demonstrate

• Phone interview led by the VP of Engineering or a lead engineer focusing on past experience and core technical concepts
• Depth in JavaScript

How to prepare

• Be able to walk your CV end to end in two minutes, and say why this company specifically.
• Have your salary expectations, notice period and location constraints ready, and ask for the rest of the loop in writing.

Onsite Loop

Highly interactive sessions featuring coding challenges, system design discussions, and a collaborative team exercise.

What to demonstrate

• Highly interactive sessions featuring coding challenges, system design discussions, and a collaborative team exercise
• Depth in JavaScript

How to prepare

• Answer aloud and timed: What is the difference between synchronous and asynchronous execution, and how do promises resolve under the hood?
• Answer aloud and timed: How would you design a system to ensure that multiple backend processes do not work on or modify the same piece of data simultaneously?

Where candidates lose points

Prioritize Communication Over Perfection

During technical discussions and coding exercises, explain your thought process out loud. The interviewers care more about how you approach a problem and handle ambiguity than whether you get every answer perfect.

Be prepared to discuss your past projects in deep detail

The engineering leadership values real-world problem-solving over abstract puzzle-solving.

Brush Up on Core JavaScript Trivia

Do not overlook the basics. Be ready to answer questions about closures, the event loop, promises, and React lifecycle methods, as these are frequently tested in the early rounds.

Questions & practice

How does the event loop work in JavaScript, and how does it handle asynchronous operations?

Medium · Frontend & JavaScript Trivia

Approach

1. Say what the runtime actually does before reasoning about the code.
2. Name what is shared across threads and what owns each piece of state.
3. Identify the window where an invariant is briefly untrue.
4. Distinguish a value from a reference to it, and say which one you handed out.

Follow-up

• What happens if two callers reach this at the same time?
• Where could this allocate more than you expect?

Explain the concept of closures in JavaScript and provide a practical use case for them.

Medium · Frontend & JavaScript Trivia

Approach

1. Say what the runtime actually does before reasoning about the code.
2. Name what is shared across threads and what owns each piece of state.
3. Identify the window where an invariant is briefly untrue.
4. Distinguish a value from a reference to it, and say which one you handed out.

Follow-up

• What happens if two callers reach this at the same time?
• Where could this allocate more than you expect?

What is the difference between synchronous and asynchronous execution, and how do promises resolve under the h

Medium · Frontend & JavaScript Trivia

What is the difference between synchronous and asynchronous execution, and how do promises resolve under the hood?

Approach

1. Say what the runtime actually does before reasoning about the code.
2. Name what is shared across threads and what owns each piece of state.
3. Identify the window where an invariant is briefly untrue.
4. Distinguish a value from a reference to it, and say which one you handed out.

Follow-up

• What happens if two callers reach this at the same time?
• Where could this allocate more than you expect?

How would you structure a localized data delivery system to minimize latency for users accessing the platform

Medium · System Design & Architecture

How would you structure a localized data delivery system to minimize latency for users accessing the platform from different geographic regions?

Approach

1. Restate the input: its shape, its size, and what is guaranteed about it.
2. Name the brute-force solution and its complexity before improving on it.
3. Choose the data structure from the access pattern, not from familiarity.
4. State the target complexity and say which constraint rules the naive version out.

Follow-up

• How does this change if the input no longer fits in memory?
• What is the worst case, and how likely is it on real data?

Find version gaps and relay lag with window functions

Medium · window functions · event tables · frame semantics

outbox_event holds event_id, aggregate_type, aggregate_id, aggregate_version, event_type, payload, status ('pending','published','dead'), attempts, created_at, published_at. A projection is missing rows and you must decide whether the relay skipped events or the consumer dropped them. Write three queries over the last seven days: one listing every aggregate_id whose published aggregate_version sequence has a hole, one giving per-day counts with a running total, and one returning the newest published event per aggregate. For each, say where the window function is evaluated relative to WHERE and LIMIT. PostgreSQL 16.

Approach

1. Gaps: compute lead(aggregate_version) OVER (PARTITION BY aggregate_id ORDER BY aggregate_version) in a subquery, then filter next_version <> aggregate_version + 1 in the outer query. Window functions are evaluated after WHERE, GROUP BY and HAVING and before the outer ORDER BY and LIMIT, so the predicate cannot sit in the same WHERE clause and PostgreSQL 16 has no QUALIFY.
2. Say what the seven-day filter does to the answer: it truncates every partition, so the first row per aggregate has no predecessor inside the window and a hole spanning the boundary is invisible. Widen the window, or join to resource.version as the authority for the true maximum.
3. Running total: SELECT date_trunc('day', created_at) AS d, count() AS n, sum(count()) OVER (ORDER BY date_trunc('day', created_at) ROWS UNBOUNDED PRECEDING). An aggregate inside a window call is legal because grouping runs before windowing. The grouping key is unique per row here so ROWS and RANGE agree, but write the frame anyway — over ungrouped rows with tied timestamps the default RANGE frame pulls in every peer row and the total jumps.
4. Newest per aggregate: DISTINCT ON (aggregate_id) ... ORDER BY aggregate_id, aggregate_version DESC is the cheap PostgreSQL-only form when an index matches that order; row_number() OVER (PARTITION BY aggregate_id ORDER BY aggregate_version DESC) = 1 is the portable form and needs a subquery for the same evaluation-order reason as the gap query.

Follow-up

• Relay failover redelivers events. Does a duplicate break the gap query, and how would you detect one from this table alone?
• Turn the gap check into a continuous monitor rather than a query someone runs after an incident. What does it watch?

Keep soft-deleted accounts from blocking re-registration

Easy · soft delete · unique constraints · engine differences

app_user holds user_id, tenant_id, email CITEXT, password_hash (NULL for SSO principals), email_verified_at, auth_version, status ('invited','active','suspended','deactivated'), created_at, updated_at, deleted_at. Two live accounts for one address inside a tenant must be impossible, but an address freed by a soft delete must be reusable, and the same tenant may delete and re-register it repeatedly. Write the uniqueness DDL for PostgreSQL 16, then the equivalent for MySQL 8 where partial indexes do not exist, and say what each permits once three deleted rows already hold that address.

Approach

1. Start from what is actually unique: not (tenant_id, email), but (tenant_id, email) among live rows. PostgreSQL says that directly — CREATE UNIQUE INDEX app_user_live_email ON app_user (tenant_id, email) WHERE deleted_at IS NULL. A full constraint over the same two columns burns the address permanently the first time someone deletes an account.
2. Keep case-insensitivity in the type or the index, never in the application: CITEXT as given, or UNIQUE (tenant_id, lower(email)) as an expression index where the extension is unavailable. A case-sensitive unique column is exactly how two accounts for one human appear.
3. For MySQL 8 the predicate has to move inside the key: add a discriminator column that is a constant 0 while the row is live and is set to user_id on delete, with UNIQUE (tenant_id, email, deleted_marker). Live rows share the constant and still collide; deleted rows differ from each other and stop colliding.
4. State the NULL variant and its dependency: leaving the marker NULL for deleted rows also works, because a unique index treats NULLs as distinct — true in MySQL, and true in PostgreSQL only under the default NULLS DISTINCT, which PostgreSQL 15 lets you reverse. Check the polarity against the three existing deleted rows: constant-on-live is what preserves the collision you want, and reversing it silently admits duplicate live accounts.

Follow-up

• A deleted account re-registers with the same address the next day. Do the old resource rows follow the new user_id, and how does the API keep the two principals apart?
• How do you honour an erasure request while resource_revision.actor_user_id still references this table?

What are the primary differences between state and props in React, and how do you optimize component rendering

Medium · Frontend & JavaScript Trivia

What are the primary differences between state and props in React, and how do you optimize component rendering?

Approach

1. Clarify what is being asked and what a complete answer contains.
2. State your assumptions explicitly before working the problem.
3. Say what you would check first and why it is the highest-information step.
4. Work from the requirement backwards to the design.

Follow-up

• What assumption would you test first?
• How would you know your answer was wrong?

How do you manage global state in a large-scale React application, and what are the trade-offs of your chosen

Medium · Frontend & JavaScript Trivia

How do you manage global state in a large-scale React application, and what are the trade-offs of your chosen approach?

Approach

1. Clarify what is being asked and what a complete answer contains.
2. State your assumptions explicitly before working the problem.
3. Say what you would check first and why it is the highest-information step.
4. Work from the requirement backwards to the design.

Follow-up

• What assumption would you test first?
• How would you know your answer was wrong?

How would you design a system to ensure that multiple backend processes do not work on or modify the same piec

Medium · System Design & Architecture

How would you design a system to ensure that multiple backend processes do not work on or modify the same piece of data simultaneously?

Approach

1. Fix the scope first: who calls this, how often, and what they do when it fails.
2. Name the read and write paths separately; they rarely have the same bottleneck.
3. Choose a partition key and say what query it makes expensive.
4. State the consistency you need, and where you are willing to be stale.

Follow-up

• What breaks first when traffic grows ten times?
• How does this behave when that dependency is down for an hour?

Explain the difference between several common design patterns (e.g., Singleton, Factory, Observer) and when yo

Medium · System Design & Architecture

Explain the difference between several common design patterns (e.g., Singleton, Factory, Observer) and when you would apply them.

Approach

1. Fix the scope first: who calls this, how often, and what they do when it fails.
2. Name the read and write paths separately; they rarely have the same bottleneck.
3. Choose a partition key and say what query it makes expensive.
4. State the consistency you need, and where you are willing to be stale.

Follow-up

• What breaks first when traffic grows ten times?
• How does this behave when that dependency is down for an hour?

Describe a scenario where you had to refactor a monolithic architecture into microservices. What challenges di

Medium · System Design & Architecture

Describe a scenario where you had to refactor a monolithic architecture into microservices. What challenges did you face with data consistency?

Approach

1. Fix the scope first: who calls this, how often, and what they do when it fails.
2. Name the read and write paths separately; they rarely have the same bottleneck.
3. Choose a partition key and say what query it makes expensive.
4. State the consistency you need, and where you are willing to be stale.

Follow-up

• What breaks first when traffic grows ten times?
• How does this behave when that dependency is down for an hour?

Walk us through a mock feature build: how would you identify the technical requirements and break them down in

Medium · Collaborative Planning & Problem-Solving

Walk us through a mock feature build: how would you identify the technical requirements and break them down into actionable tasks?

Approach

1. Clarify what is being asked and what a complete answer contains.
2. State your assumptions explicitly before working the problem.
3. Say what you would check first and why it is the highest-information step.
4. Work from the requirement backwards to the design.

Follow-up

• What assumption would you test first?
• How would you know your answer was wrong?

How do you estimate the effort required for a specific feature, and what criteria do you use to assign point v

Medium · Collaborative Planning & Problem-Solving

How do you estimate the effort required for a specific feature, and what criteria do you use to assign point values during sprint planning?

Approach

1. Clarify what is being asked and what a complete answer contains.
2. State your assumptions explicitly before working the problem.
3. Say what you would check first and why it is the highest-information step.
4. Work from the requirement backwards to the design.

Follow-up

• What assumption would you test first?
• How would you know your answer was wrong?

Exports duplicate a row range about once a week

Hard · leases · clock skew · idempotency

Roughly once a week an export writes a file containing a duplicated range of rows. The affected job_run rows show attempt = 1, status = succeeded, one started_at, and a lease_owner naming a different host from the one whose logs show the job starting. Leases last 30 seconds and are heartbeated every 10 from inside the handler; lease_expires_at is computed on the worker and compared against the database's now(). Find the mechanism, and give a fix that holds even if you cannot fix the clocks.

Approach

1. Start from the fact that eliminates the obvious answer. attempt = 1 means no retry was recorded, so this is not a re-run after failure; two workers ran the same row concurrently and the takeover path never touched the counter. lease_owner naming a host other than the one that started the job is the same statement from the other side.
2. Enumerate the mechanisms that cause a premature takeover, then find the signal that separates them. Either the lease genuinely expired because the heartbeat did not fire, which is what happens when the heartbeat runs on the handler's own thread and the handler makes a long blocking call, or it only appeared expired because two clocks disagree, since lease_expires_at is written from the worker's clock and evaluated against the database's. The discriminator is the distribution: incidents clustered on the longest exports indict the heartbeat, incidents clustered on one host indict skew. Measure both, and measure each host's offset against the database directly.
3. Read the reclaim query precisely. In PostgreSQL now() is transaction start time, not statement time, so a reclaimer holding a long transaction compares against an older timestamp than expected; clock_timestamp() is the statement-time function. This is worth ruling in or out before you redesign anything, because it changes which rows look expired.
4. Remove the second clock rather than trying to synchronise it. Issue and extend the lease in the database, with lease_expires_at = now() + interval '30 seconds' in both the claim and the heartbeat, so exactly one clock is ever compared and worker skew stops mattering to this predicate.

Follow-up

• The displaced worker has already streamed half the file to object storage. What makes that side effect safe to repeat?
• You now count takeovers. What alert fires on that counter, and at what threshold?

Suggested practice checklist

Built from the rounds and topics Neighborhoods candidates report.

Day 1 — Map the Neighborhoods loop

• Write out the reported sequence: Recruiter Screen, Technical Phone Screen, Onsite Loop.
• For each round, write one sentence on what it is judging, from the description above, and mark the one you are least ready for.

Deliverable: A one-page map of the 3 reported rounds, with the weakest marked.

Day 2 — Work JavaScript

• Spend the session on JavaScript, which Neighborhoods candidates report being tested on.
• Write one worked example in JavaScript and time yourself on it.

Deliverable: One timed worked example in JavaScript.

Day 3 — Work React

• Spend the session on React, which Neighborhoods candidates report being tested on.
• Write one worked example in React and time yourself on it.

Deliverable: One timed worked example in React.

Day 4 — Work Frontend Development

• Spend the session on Frontend Development, which Neighborhoods candidates report being tested on.
• Write one worked example in Frontend Development and time yourself on it.

Deliverable: One timed worked example in Frontend Development.

Day 5 — Answer out loud: Frontend & JavaScript Trivia

• Answer aloud, timed: How does the event loop work in JavaScript, and how does it handle asynchronous operations?
• Answer aloud, timed: What are the primary differences between state and props in React, and how do you optimize component rendering?

Deliverable: Spoken answers to 2 reported Frontend & JavaScript Trivia question(s), under time.

Day 6 — Answer out loud: System Design & Architecture

• Answer aloud, timed: How would you design a system to ensure that multiple backend processes do not work on or modify the same piece of data simultaneously?
• Answer aloud, timed: Explain the difference between several common design patterns (e.g., Singleton, Factory, Observer) and when you would apply them.

Deliverable: Spoken answers to 2 reported System Design & Architecture question(s), under time.

Day 7 — Answer out loud: Collaborative Planning & Problem-Solving

• Answer aloud, timed: Walk us through a mock feature build: how would you identify the technical requirements and break them down into actionable tasks?
• Answer aloud, timed: How do you estimate the effort required for a specific feature, and what criteria do you use to assign point values during sprint planning?

Deliverable: Spoken answers to 2 reported Collaborative Planning & Problem-Solving question(s), under time.

Behavioural preparation

Behavioural rounds judge the decision you made and what it cost.

Describe a time when you had to make a technical compromise to meet a tight product deadline. How did you mana

Medium · Collaborative Planning & Problem-Solving

Describe a time when you had to make a technical compromise to meet a tight product deadline. How did you manage technical debt?

Approach

1. Pick a story where you made the decision, not one where you watched it.
2. State the situation in two sentences and spend the rest on the reasoning.
3. Give the blast radius: what could have broken, and what you measured.
4. Name the disagreement and how you resolved it with evidence.

Follow-up

• What would you do differently if you ran that again?
• How did you know your change caused the improvement?

How do you handle a situation where a team member disagrees with your architectural approach during a planning

Medium · Collaborative Planning & Problem-Solving

How do you handle a situation where a team member disagrees with your architectural approach during a planning session?

Approach

1. Pick a story where you made the decision, not one where you watched it.
2. State the situation in two sentences and spend the rest on the reasoning.
3. Give the blast radius: what could have broken, and what you measured.
4. Name the disagreement and how you resolved it with evidence.

Follow-up

• What would you do differently if you ran that again?
• How did you know your change caused the improvement?

Walk me through one of the personal or professional projects on your resume. What was the biggest technical ch

Medium · Behavioral & Experience Review

Walk me through one of the personal or professional projects on your resume. What was the biggest technical challenge you faced, and how did you overcome it?

Approach

1. Pick a story where you made the decision, not one where you watched it.
2. State the situation in two sentences and spend the rest on the reasoning.
3. Give the blast radius: what could have broken, and what you measured.
4. Name the disagreement and how you resolved it with evidence.

Follow-up

• What would you do differently if you ran that again?
• How did you know your change caused the improvement?

Tell me about a time you introduced a new tool or methodology to your engineering team. What was the impact, a

Medium · Behavioral & Experience Review

Tell me about a time you introduced a new tool or methodology to your engineering team. What was the impact, and how did you drive adoption?

Approach

1. Pick a story where you made the decision, not one where you watched it.
2. State the situation in two sentences and spend the rest on the reasoning.
3. Give the blast radius: what could have broken, and what you measured.
4. Name the disagreement and how you resolved it with evidence.

Follow-up

• What would you do differently if you ran that again?
• How did you know your change caused the improvement?

How do you stay current with rapidly evolving frontend and backend technologies, and how do you decide when to

Medium · Behavioral & Experience Review

How do you stay current with rapidly evolving frontend and backend technologies, and how do you decide when to adopt them?

Approach

1. Pick a story where you made the decision, not one where you watched it.
2. State the situation in two sentences and spend the rest on the reasoning.
3. Give the blast radius: what could have broken, and what you measured.
4. Name the disagreement and how you resolved it with evidence.

Follow-up

• What would you do differently if you ran that again?
• How did you know your change caused the improvement?