Example: How to write an image from data URI and read it.

example-data-uri-image-write-read.js

const fs = require('fs');

const dataUri = "data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAAUAAAAFCAYAAACNbyblAAAAHElEQVQI12P4//8/w38GIAXDIBKE0DHxgljNBAAO9TXL0Y4OHwAAAABJRU5ErkJggg==";
const outputFilename = "output";

writeImage(dataUri, outputFilename);
readImage(outputFilename + ".png");

function writeImage(dataUri, outputFilename) {
  const regex = /^data:.+\/(.+);base64,(.*)$/;
  const matches = dataUri.match(regex);
  const ext = matches[1];
  const data = matches[2];
  const buffer = new Buffer(data, 'base64');
  const outputFilepath = outputFilename + '.' + ext;
  fs.writeFileSync(outputFilepath, buffer);
  console.log(`*** Image wrote
    From dataURI: "${dataUri}" 
    To file => "${outputFilepath}"`);
}

function readImage(file) {
  // read binary data
  const bitmap = fs.readFileSync(file);
  // convert binary data to base64 encoded string
  const base64str = new Buffer(bitmap).toString('base64');
  console.log(`*** Image read
    From file: "${file}"
    To base64 => "${base64str}"`);
}

/* Log output:
$ node example-data-uri-image-write-read.js
*** Image wrote
    From dataURI: "data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAAUAAAAFCAYAAACNbyblAAAAHElEQVQI12P4//8/w38GIAXDIBKE0DHxgljNBAAO9TXL0Y4OHwAAAABJRU5ErkJggg==" 
    To file => "output.png"
*** Image read
    From file: "output.png"
    To base64 => "iVBORw0KGgoAAAANSUhEUgAAAAUAAAAFCAYAAACNbyblAAAAHElEQVQI12P4//8/w38GIAXDIBKE0DHxgljNBAAO9TXL0Y4OHwAAAABJRU5ErkJggg=="
*/