What is LeanJS?

LeanJS is a stack of solutions for building scalable front-end applications. These solutions integrate with existing technology, and can be grouped in the following six layers to build a full micro-frontends architecture:

┌────────────────────┐
│     Deployment     │  AWS
└────────────────────┘
┌────────────────────┐
│     Workspace      │  Turborepo, Lerna
└────────────────────┘
┌────────────────────┐
│      Routing       │  Nextjs, Vue Router, React Router
└────────────────────┘
┌────────────────────┐
│  App composition   │  React, Vue
└────────────────────┘
┌────────────────────┐
│   Shared runtime   │  Vue, React
└────────────────────┘
┌────────────────────┐
│    Shared code     │  Webpack Module Federation
└────────────────────┘

What are micro-frontends?

Micro-frontends is a software architecture for building distributed frontend applications. In this architecture, a frontend application is composed of smaller frontend applications. We believe that successful micro-frontend implementations are LEAN:

1. Loosely coupled
2. Executed independently
3. Autonomously developed and managed by a small team
4. Narrowed to a business domain

Hence the name LeanJS.

tip

Micro-frontends help organisations scale engineers. Its benefits don't correlate with the size of the codebase but with the number of engineers working on it.

Micro-frontends don't solve technical problems, they solve people problems.

You may not need micro-frontends

Micro-frontends help break up Web-based products into smaller independent ones that can be developed, deployed, and run by small independent groups of people.

That's typically a requirement when an organisation wants to develop more features faster but incrementing the number of engineers contributing to a product doesn't increment the output proportionally. In other words, they fail to scale people.

You don't need micro-frontends if:

• You don't have problems scaling engineers.
• You have one team or a few small ones.
• Your lead time, code to market, and mean time to recovery metrics are fine.
• You want to avoid the increased complexity in observability, releasing, testing, etc of running distributed systems.

The good news is, you can still use LeanJS to build the foundation of a distributed architecture without fully committing to it. You may start using LeanJS app composition layer and shared runtime layer, and never go all the way to independent deployments - also known as micro-frontends. A modular monolith is more scalable than a monolithic big ball of mug.

Why another Framework?

LeanJS is born from the need to break up monolithic front-end applications in different companies. Most micro-frontend projects start by breaking up an existing monolith rather than building a brand new product using micro-frontends from the start.

Although most micro-frontend architectures will face similar problems, every front-end monolith has its own requirements and tech stack. That's why many organisations - Amex, Hopin, DAZN, Netflix, Cazoo, Zalando - end up building their own solutions instead of using off the shelf micro-frontends solutions.

That's not to say that existing micro-frontend frameworks don't work. Your requirements might be implemented using frameworks such as single-spa, like IG did.

We believe that organisations should be able to incrementally integrate and reuse solutions within their unique monoliths without reinventing them. LeanJS is not a single, standalone framework. It's an opinionated stack of solutions that you can reuse to build your own stack.