µJS: 5KB AJAX library alternative to Htmx and Turbo

What it does

µJS is a lightweight AJAX library that intercepts link clicks and form submissions, then fetches and displays new pages without a full browser reload. It replaces only the DOM fragments that have changed, creating the feel of a single-page application. The library works with any server-side technology—PHP, Python, Ruby, Go, Node.js—and requires no backend modifications. It includes features like prefetch on hover, a built-in progress bar, patch mode for updating multiple fragments in one request, Server-Sent Events support, DOM morphing, View Transitions, and HTTP verb support (GET, POST, PUT, PATCH, DELETE) on any element.

Who it is for

This targets builders maintaining traditional server-rendered websites who want faster navigation without adopting a JavaScript framework or build step. Founders considering AJAX solutions should note µJS explicitly positions itself as an alternative to HTMX and Turbo. It appeals to teams using lightweight backend stacks where simplicity matters more than framework integration.

Pricing

The site does not show prices. The library is MIT licensed.

How it stands out

Size is the primary differentiator. µJS is 5KB gzipped compared to HTMX at 16KB and Turbo at 25KB. The creator emphasizes no dependencies, no build step, and no server changes—truly drop-in compatibility. It uses the modern Fetch API with native AbortController instead of XMLHttpRequest, and supports emerging features like View Transitions and DOM morphing via idiomorph.

What a founder should check

First, test whether the size advantage matters in practice. HTMX's larger bundle might include capabilities µJS doesn't expose, making smaller package size misleading if features get added later. Second, examine the switching cost: both HTMX and Turbo have established communities, documentation, and integrations with popular frameworks. Verify whether µJS's zero-dependency approach becomes a liability as you need monitoring, error handling, or analytics. Third, understand the moat—without a framework lock-in or paid hosting tier, the library competes entirely on technical merit. Check whether the creator plans commercial services or if this remains a permanent open-source project.

Thinking of building something like this?

Every launch here is a competitor to somebody's idea. If yours is close, check it against the market before you build: the Full Check names the rivals, the prices and the gaps.