Sends response with prism wrapped gist code

code.js

const fetch = require('isomorphic-unfetch')
const { json, send } = require('micro') 
const { readFileSync } = require('fs')
const { resolve } = require('path')

// read template once
const template = readFileSync(resolve(__dirname, './static/code.html'), 'utf8');

// encode html entities
const entities = {'&': '&amp;', '<': '&lt;', '>': '&gt;'};
const replaceTag = tag => entities[tag] || tag
const htmlEntities = str => str.replace(/[&<>]/g, replaceTag)

// these help with <pre> whitespace issues and keeping lines under 80 char
const pre = c => `<pre>${c}</pre>`
const code = (c, lang = 'js') => `<code class="language-${lang}">${c}</code>`
const getJson = url => fetch(url).then(res => res.json())

module.exports = async (req, res) => {
  const id = req.url.split('/').pop()
  if (id === 'favicon.ico') return send(res, 404)
  const { files } = await getJson(`https://api.github.com/gists/${id}`)
  const source = Object.entries(files).reduce((source, [name, info]) => {
    const file = `
      <pre>${name}</pre>
      ${pre(code(htmlEntities(info.content), info.language.toLowerCase()))}
    `
    return source + file
  }, '') 
  send(res, 200, template + source)
}