install.js

#!/usr/bin/env node

// maintainer note - x.y.z-ab version in package.json -> x.y.z
var version = require('./package').version.replace(/-.*/, '')

var fs = require('fs')
var os = require('os')
var path = require('path')
var extract = require('extract-zip')
var download = require('electron-download')

var arch = 'x64'
var platform = os.platform()

function onerror (err) {
  throw err
}

var paths = {
  darwin: path.join(__dirname, './dist/Electron.app/Contents/MacOS/Electron'),
//  linux: path.join(__dirname, './dist/electron'), // Unity WebPlayer not supported
  win32: path.join(__dirname, './dist/electron.exe')
}

if (!paths[platform]) throw new Error('Unknown platform: ' + platform)

// while 64 bit Unity WebPlayer exists on Windows, it is not as 
// stable and has a constant watermark in the bottom right corner
if (platform == 'win32') arch = 'ia32';

// downloads if not cached
download({version: version, arch: arch}, extractFile)

// unzips and makes path.txt point at the correct executable
function extractFile (err, zipPath) {
  if (err) return onerror(err)
  fs.writeFile(path.join(__dirname, 'path.txt'), paths[platform], function (err) {
    if (err) return onerror(err)
    extract(zipPath, {dir: path.join(__dirname, 'dist')}, function (err) {
      if (err) return onerror(err)
    })
  })
}