siteslimmer/src/subsetFont.js

A tool to optimize built files including HTML, CSS, JS, and fonts.

import { promises as fs } from 'fs'
import path from 'path'
import { createRequire } from 'module'

const require = createRequire(import.meta.url)
const subsetFont = require('subset-font')

export const subsetFontFile = async (filePath, text) => {
	const fontData = await fs.readFile(filePath)

	const subsettedFont = await subsetFont(fontData, text, {
		formats: [path.extname(filePath).slice(1)], 
	})

	const originalSize = fontData.length
	const newSize = subsettedFont.length

	let savings = 0
	if (newSize < originalSize) {
		await fs.writeFile(filePath, subsettedFont)
		savings = originalSize - newSize
	}

	return { originalSize, newSize, savings }
}

export const getUniqueCharactersFromFiles = async (filePaths) => {
	let uniqueChars = new Set()

	for (const filePath of filePaths) {
		const data = await fs.readFile(filePath, 'utf8')

		for (const char of data) {
			uniqueChars.add(char)
		}
	}

	return Array.from(uniqueChars).join('')
}