CODE EXAMPLE FOR TYPESCRIPT

Get MIME Type from Base64 string

var signatures = {
  JVBERi0: "application/pdf",
  R0lGODdh: "image/gif",
  R0lGODlh: "image/gif",
  iVBORw0KGgo: "image/png",
  "/9j/": "image/jpg"
};

function detectMimeType(b64) {
  for (var s in signatures) {
    if (b64.indexOf(s) === 0) {
      return signatures[s];
    }
  }
}

// Some tests
console.log(detectMimeType('R0lGODdhAQABAPAAAP8AAAAAACwAAAAAAQABAAACAkQBADs='));
console.log(detectMimeType('iVBORw0KGgoAAAANSUhEUgAAAAEAAAABCAIAAACQd1PeAAAADElEQVR42mP4z8AAAAMBAQD3A0FDAAAAAElFTkSuQmCC'));
console.log(detectMimeType('JVBERi0xLjUKJYCBgoMKMSAwIG9iago8PC9GaWx0ZXIvRmxhdGVEZWNvZGUvRmlyc3QgMTQxL04gMjAvTGVuZ3'));
console.log(detectMimeType('/9j/4AAQSkZJRgABAQAAZABkAAD/2wCEABQQEBkSGScXFycyJh8mMi4mJiYmLj41NTU1NT5EQUFBQUFBRERERERERERE'));
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