Deep dives into the Pretext text layout library — how it works, what you can build, and real-world performance benchmarks.
The tools that power the best-performing video ads in 2026 have roots in something unexpected: real-time text layout and creative typography. From kinetic text animations to AI-generated talking-head videos, the line between developer tooling and marketing technology has never been blurrier.
Pretext is a pure JavaScript/TypeScript library for multiline text measurement and layout, created by Cheng Lou (former React core team member and creator of react-motion). It measures and lays out text without ever touching the DOM — making it up to 500x faster than traditional browser layout metho
Pretext's public API consists of core text measurement and layout functions: prepare(), layout(), prepareWithSegments(), layoutWithLines(), and utility functions for advanced use cases. The simplicity of the core interface hides a thoughtful internal architecture designed to make text layout fast en
What happens when you can layout text in ~0.09ms instead of 30ms? Among other things: you can build games where every single game element is made of characters — and it runs at 60fps without breaking a sweat.
Performance claims in JavaScript are easy to make and hard to trust. "300x faster" sounds like marketing copy — so let's look at what's actually happening, why DOM text measurement is slow, and what the real numbers look like when you compare Pretext to the traditional approach.
When Pretext hit 7,000 GitHub stars in its first three days — now grown to 29,500+ — developers didn't just star the repo — they started building. The pretext.cool community showcase now hosts 17 interactive demos from developers around the world, each exploring a different dimension of what becomes
Pretext (@chenglou/pretext) is a TypeScript library for measuring and laying out text without the DOM. This guide walks you through installation, your first layout, and rendering to the screen — all in under 5 minutes.
在 Web 的大部分历史里，"测量一段文本的尺寸"只有一种做法：把它塞进 DOM，调用 getBoundingClientRect() 让浏览器算。能用，但每次调用都会触发一次 layout reflow —— 而 reflow 是客户端渲染中单次开销最大的操作。Pretext 由 Cheng Lou（React 核心团队前成员、react-motion 作者，曾参与 ReScript、Midjourney）设计，给出了完全不同的答案：把文本布局当作纯算术运算来做，从头到尾不碰 DOM。
For most of the web's history, "measuring text" has meant one thing: stick a <span> in the document, read its getBoundingClientRect(), and let the browser do the layout work. It works — but it forces a layout reflow every time you ask, and that reflow is the single most expensive operation in client