"dependencies": {
 "canvas": "^1.6.7",
 "puppeteer": "^0.12.0",
 "resemblejs": "^2.2.6"
}

const fs = require('fs')
const puppeteer = require('puppeteer')
const resemble = require('resemblejs')
const Canvas = require('canvas')

const URL = 'xxx' // 验证码页面访问地址
const width = 600
const height = 400
const slider_width = 44

const sleep = duration => {
 return new Promise(resolve => {
 setTimeout(resolve, duration)
 })
}

const browser = await puppeteer.launch()
const page = await browser.newPage()
page.setViewport({width, height})

await page.goto(URL, {
 waitUntil: 'networkidle'
})

const offset = await page.evaluate(() => {
 let offset_ifr = $('iframe').offset()

 return {
 top: offset_ifr.top + 222,
 left: offset_ifr.left + 10
 }
})

await page.mouse.move(offset.left + 10, offset.top + 10)
// 按下鼠标
await page.mouse.down({
 button: 'left'
})
// 等待图片出现
await sleep(500)
// 截图
await page.screenshot({path: 'screenshot2.png'})

await page.mouse.up({
 button: 'left'
})
// 等待图片出现
await sleep(500)
// 截图
await page.screenshot({path: 'screenshot3.png'})

await new Promise(resolve => {
 resemble.outputSettings({
 transparency: 0
 })
 resemble('screenshot2.png')
 .compareTo('screenshot3.png')
 .ignoreColors()
 .onComplete(data => {
  fs.writeFileSync('diff.png', data.getBuffer())
  resolve()
 })
})

const getDestinationX = min_x => {
 const canvas = new Canvas(width, height)
 const ctx = canvas.getContext('2d')
 const buf = fs.readFileSync('diff.png')
 const img = new Canvas.Image()
 img.src = buf
 ctx.drawImage(img, 0, 0, width, height)
 const img_data = ctx.getImageData(0, 0, width, height).data

 let destination_x = -1

 for (let y = 0; y < height; y++) {
 for (let x = width; x >= min_x; x--) {
  let p = width * y + x
  p = p << 2
  if (img_data[p + 3] === 255 && img_data[p - 10 * 4 + 3] === 255) {
  destination_x = x
  break
  }
 }
 if (destination_x > -1) break
 }

 return destination_x - slider_width
}