Create Image from buffer and save to destination folder

app.js

const watermark = require('./watermark');
const path = `assets/target.png`;
const w = 500;
const h = 500;
watermark.drawWatermarkAsBuffer(path, './assets/watermark_source.png', w, h).then(buffer => {
      require("fs").writeFile("assets/output.png", buffer, 'base64', function(err) {
        console.log(err);
      });
});