fetch_blob.js

var url = 'https://ronreiter-meme-generator.p.mashape.com/meme?meme=Baby+Godfather&font_size=50&font=Impact&top=Thanks+m&bottom=Later';
var headers = new Headers({'X-Mashape-Key': 'API_KEY'});
var options = {
  method: 'GET',
  headers: headers,
  mode: 'cors',
  cache: 'default'
};
var request = new Request(url);

fetch(request, options).then((response) => {
  response.arrayBuffer().then((buffer) => {
    var base64Flag = 'data:image/jpeg;base64,';
    var imageStr = arrayBufferToBase64(buffer);

    document.querySelector('img').src = base64Flag + imageStr;
  });
});

function arrayBufferToBase64(buffer) {
  var binary = '';
  var bytes = [].slice.call(new Uint8Array(buffer));

  bytes.forEach((b) => binary += String.fromCharCode(b));

  return window.btoa(binary);
};