JSFiddle - React, Tailwind, and code Playground

HTML

<h1>
Does it have CIA hidden data?
</h1>
<h2 style="color:red;">
<div id="result"></div>
</h2>
<input type="file" />

JavaScript

var NULL_BYTE_COUNT = 30;

document.querySelector('input').addEventListener('change', function() {

  var reader = new FileReader();
  reader.onload = function() {

    var array = new Uint8Array(this.result);
    var nullByteCount = 0;
    var numHiddenFiles = 0;

    for (var i = 0; i < array.length; i++) {
      var inc = array[i] === 0x0 ? 1 : -1;
      nullByteCount = Math.max(nullByteCount + inc, 0);
      if (nullByteCount === NULL_BYTE_COUNT) {
        numHiddenFiles++;
        nullByteCount = 0;
      }
    }

    var answer = "No, try another file.";
    if (numHiddenFiles > 0) {
      answer = "Yes, there are " + numHiddenFiles + " chunks of hidden data.";
    }
    document.getElementById("result").innerHTML = answer;
  }
  reader.readAsArrayBuffer(this.files[0]);

}, false);