node-pretext

Server-side text measurement for Node.js. Accurate font-aware width/height calculation without a browser.

The missing piece for programmatic layout generation — SVG, PDF, Canvas, Excalidraw, card images, OG images, slides, and anything else where you need to know how wide text is before placing it.

Why

Browsers have measureText(). Servers don't. If you're generating layouts programmatically (diagrams, images, PDFs), you need to know text dimensions to align elements. Without accurate measurement, text overflows boxes, labels misalign, and centering is guesswork.

node-pretext uses node-canvas to access the OS font engine directly, giving you the same measureText() accuracy in Node.js.

Inspired by @chenglou/pretext, which solves the same problem in the browser by avoiding DOM reflow.

Install

npm install node-pretext

Usage

const { measure, width, centerX, wrap } = require('node-pretext');

// Basic width
width('Hello World', '14px Helvetica');  // 77.8

// Full metrics
measure('Hello', '20px Arial');
// { width: 47.1, ascent: 15, descent: 4, height: 19 }

// Center text at x=200
centerX('Title', '28px Helvetica', 200);  // returns left x

// Word wrap to fit 300px
wrap('Long text here...', '14px Helvetica', 300);
// { lines: [...], lineWidths: [...], totalHeight: 35 }

CLI

# Width only
npx node-pretext "14px Helvetica" "Hello World"

# Full metrics
npx node-pretext --json "20px Arial" "Hello"

# Batch (stdin)
echo '[{"font":"14px Helvetica","text":"Hello"}]' | npx node-pretext --batch

API

measure(text, font?) → { width, ascent, descent, height }

Full text metrics. Font defaults to "14px Helvetica".

width(text, font?) → number

Width only. Convenience shorthand.

measureBatch(items) → metrics[]

Measure multiple text/font pairs in one call. Input: [{ text, font? }].

centerX(text, font, cx) → number

Returns the left x coordinate to center text at cx.

centerY(font, cy) → number

Returns the top y coordinate to center text at cy.

wrap(text, font, maxWidth) → { lines, lineWidths, totalHeight }

Word-wrap text to fit within maxWidth pixels.

clearCache()

Clear the internal measurement cache.

Use Cases

• Diagram generation — Excalidraw, Mermaid, D3
• OG/social images — Blog thumbnails, Twitter cards
• Card news — Automated image content
• PDF reports — Table cell sizing, label placement
• SVG generation — Server-rendered charts and badges
• Slide decks — Programmatic presentation generation

License

MIT