@libraz/mejiro

Japanese vertical text layout engine — line breaking, kinsoku shori, and hanging punctuation for the web.

Install

npm install @libraz/mejiro
# or
yarn add @libraz/mejiro
# or
pnpm add @libraz/mejiro
# or
bun add @libraz/mejiro

Quick Start

import { MejiroBrowser } from '@libraz/mejiro/browser';

const mejiro = new MejiroBrowser({
  fixedFontFamily: '"Noto Serif JP"',
  fixedFontSize: 16,
});

// Preload font (uses instance defaults)
await mejiro.preloadFont();

// Compute effective line width for vertical layout
const lineWidth = mejiro.verticalLineWidth(containerHeight);

// Layout a single paragraph
const result = await mejiro.layout({ text: '吾輩は猫である。', lineWidth });

// Layout an entire chapter
const chapter = await mejiro.layoutChapter({
  paragraphs: [{ text: '吾輩は猫である。' }, { text: '名前はまだ無い。' }],
  lineWidth,
});

Units

All dimensional parameters — fontSize, lineWidth, containerHeight, advances, etc. — are in CSS pixels (px). This matches the unit returned by Canvas.measureText() and used by CSS layout.

Subpath Exports

| Import path | Description | |---|---| | @libraz/mejiro | Core layout engine (zero dependencies, no DOM required) | | @libraz/mejiro/browser | Font loading, measurement, and browser integration | | @libraz/mejiro/epub | EPUB parsing — extracts text and ruby annotations | | @libraz/mejiro/render | Converts layout results into framework-agnostic render data + CSS |

API Overview

MejiroBrowser

Main browser integration class. Manages font loading, width caching, and layout.

• constructor(options?) — fixedFontFamily / fixedFontSize set defaults for all methods.
• layout(options) — Compute line breaks for a single text. fontFamily / fontSize fall back to instance defaults.
• layoutChapter(options) — Lay out multiple paragraphs. fontFamily / fontSize fall back to instance defaults.
• preloadFont(fontFamily?, fontSize?) — Preload a font. Falls back to instance defaults.
• verticalLineWidth(containerHeight, fontSize?) — Effective line width for vertical text. Falls back to instance fixedFontSize.
• clearCache(fontKey?) — Clear the width measurement cache.

layoutText(options)

Standalone one-shot layout function. Creates its own font loader and measurer — no MejiroBrowser instance needed. All parameters are required.

verticalLineWidth(containerHeight, fontSize)

Standalone function to compute effective vertical line width with a safety margin.

License

MIT