Revolut Engineering

Building the Web that Moves Money

Inside Web engineering at Revolut — tech stack, architecture, culture

Canvas-based JS Blur Detection

KYC document verification — Laplacian variance, Canvas API, typed arrays

Best Practices for Unit Testing

Sample functions, MockFunc, builder pattern, AAA

Event Loop

javascript.info — Event Loop

Macrotasks, microtasks, rendering pipeline, splitting heavy tasks

Event Loop Explained with Examples

Call stack, Web APIs, callback queue, code traces

Promises & Async

javascript.info — Promise Basics

Constructor, resolve/reject, .then/.catch/.finally

javascript.info — Promise Chaining

Chaining .then, returning promises, thenable objects

javascript.info — Error Handling with Promises

Implicit try/catch, .catch placement, rethrowing

javascript.info — Promise API

Promise.all, allSettled, race, any, resolve, reject

javascript.info — Async/Await

async functions, await, error handling, parallel patterns

Fetch & Networking

javascript.info — Fetch

fetch(), Response object, headers, POST, status codes

javascript.info — Fetch: Abort

AbortController, signal, cancellation patterns

javascript.info — Fetch: CORS

Cross-origin requests, preflight, simple vs complex

JS Fundamentals

javascript.info — Closures

Lexical environment, scope chain, closure-in-loop

javascript.info — Function Binding

Losing this, bind, call, apply, partial application

javascript.info — Map and Set

Map vs Object, Set for uniqueness, iteration, conversion

javascript.info — Array Methods

map, filter, reduce, find, sort, flatMap, and more

javascript.info — Objects

Property access, this, computed properties, in operator

javascript.info — Prototypal Inheritance

[[Prototype]], __proto__, prototype chain

TypeScript

TS Handbook — Narrowing

Type guards, discriminated unions, never, control flow

TS Handbook — Generics

Generic functions, constraints, utility types

React

react.dev — Preserving and Resetting State

Keys, state identity, same position same component

react.dev — useEffect

Effects, cleanup, dependency array, lifecycle

react.dev — Synchronizing with Effects

When to use effects, not events vs effects

react.dev — Error Boundaries

getDerivedStateFromError, componentDidCatch

Testing

React Testing Library — Cheatsheet

Queries, events, async utilities, best practices

RTL — Query Priority

getByRole > getByLabelText > getByText > getByTestId