webpack loader for font subset

fontmin.js

const os = require('os')
const fs = require('fs')
const path = require('path')
const exec = require('child_process').exec

const fontsubset = function(source, text, callback) {
  const tmp = path.join(os.tmpdir(), 'tmp.ttf')
  const subset = `node_modules/fontsubset/bin/fontsubset -s ${text} ${source} ${tmp}`
  const sfntedit = path.resolve(__dirname, '../assets/font/', 'sfntedit') + ' -d vhea ' + tmp

  exec(subset, function() {
    exec(sfntedit, function() {
      fs.readFile(tmp, function(err, data) {
        callback(null, data)
      })
    })
  })
}

module.exports = function(content) {
  this.cacheable && this.cacheable();

  const callback = this.async()
  const source = this.resourcePath
  const command = 'grep -hr --include "*.js" main_title src'

  exec(command, (error, stdout, stderr) => {
    let text = stdout.split('').filter(function(s) {
          return s.charCodeAt() > 128
        }).join('')

    fontsubset(source, text, callback)
  })
}