PHP Blob을 Base64로 변환하는 방법

window.onload=function(){
window.URL = window.URL || window.webkitURL;
var fileSelect = document.getElementById("fileSelect"),
    fileElem = document.getElementById("fileElem"),
    fileList = document.getElementById("fileList");
fileSelect.addEventListener("click", function (e) {
  if (fileElem) {
    fileElem.click();
  }
  e.preventDefault(); // prevent navigation to "#"
}, false);
}
function handleFiles(files) {
  if (!files.length) {
    fileList.innerHTML = "<p>No files selected!</p>";
  } else {
    fileList.innerHTML = "";
    var list = document.createElement("ul");
    fileList.appendChild(list);
    for (var i = 0; i < files.length; i++) {
        if(files[i].size > 1000000) {
            alert(files[i].name + &#39; is too big. Please resize it and try again.&#39;);
        } else {
        var li = document.createElement("li");
      list.appendChild(li);
      var img = document.createElement("img");
      img.src = window.URL.createObjectURL(files[i]);
      img.height = 60;
      img.setAttribute("class", "shotzPrev");
      img.onload = function() {
        window.URL.revokeObjectURL(this.src);
      }
      li.appendChild(img);
      var info = document.createElement("span");
      info.innerHTML = files[i].name + "<br>" + files[i].size + " bytes";
      li.appendChild(info);
        }
    }
  }
}

fetch("/path/to/server", {
  method: "POST"
  body: files[i]
})
.then(response => console.log(response.ok))
.catch(err => console.error(err));