最近项目有个功能，更换用户个人头像，裁剪后上传保存。裁剪用了cropper.js，裁剪后的图片为base64编码格式，传到node中，进行转换成图片在保存到数据库中，代码如下：

const express = require("express");
const router = express.Router();
const fs = require('fs-extra')
const path = require("path");
router.post('/topng', (req, res, next) => {
  let { imgUrl } = req.body; 
  if (imgUrl) {
    const fileName = Date.now() + '.png';
    const base64 = imgUrl.replace(/^data:image\/\w+;base64,/, "");//去掉图片base64码前面部分data:image/png;base64
    const dataBuffer = Buffer.from(base64,'base64'); //把base64码转成buffer对象，
    let pwd = path.join(__dirname, `../img.png`);
    fs.outputFile(pwd, dataBuffer, { overwrite: true }, function (err) {//用fs写入文件
      if (err) {
        console.log(err);
        res.json({ result: false, code: 500, message: "图片文件上传失败！" });
      } else {
        res.json({ result: true, code: 200 });
      }
    })
  } else {
    res.json({ result: false, code: 500, message: "上传内容不能为空！" });
  }
});

module.exports = router;