1function getBase64Image(src, callback, outputFormat) {
2      const img = new Image();
3      img.crossOrigin = 'Anonymous';
4      img.onload = () => {
5        const canvas = document.createElement('canvas');
6        const ctx = canvas.getContext('2d');
7        let dataURL;
8        canvas.height = img.naturalHeight;
9        canvas.width = img.naturalWidth;
10        ctx.drawImage(img, 0, 0);
11        dataURL = canvas.toDataURL(outputFormat);
12        callback(dataURL);
13      };
14
15      img.src = src;
16      if (img.complete || img.complete === undefined) {
17        img.src = "data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///ywAAAAAAQABAAACAUwAOw==";
18        img.src = src;
19      }
20    }

1function encodeImageFileAsURL(element) {
2  var file = element.files[0];
3  var reader = new FileReader();
4  reader.onloadend = function() {
5    console.log('RESULT', reader.result)
6  }
7  reader.readAsDataURL(file);
8}
9<input type="file" onchange="encodeImageFileAsURL(this)" />

1function toDataURL(url, callback) {
2  var xhr = new XMLHttpRequest();
3  xhr.onload = function() {
4    var reader = new FileReader();
5    reader.onloadend = function() {
6      callback(reader.result);
7    }
8    reader.readAsDataURL(xhr.response);
9  };
10  xhr.open('GET', url);
11  xhr.responseType = 'blob';
12  xhr.send();
13}
14
15toDataURL('https://cdn.discordapp.com/attachments/571092147801948204/784586541146177606/6f32c864-985a-481d-8d8e-bd1f14ab9951.png', function(dataUrl) {
16  console.log('RESULT:', dataUrl)
17})

1<input id="inputFileToLoad" type="file" onchange="encodeImageFileAsURL();" />
2<div id="imgTest"></div>
3<script type='text/javascript'>
4  function encodeImageFileAsURL() {
5
6    var filesSelected = document.getElementById("inputFileToLoad").files;
7    if (filesSelected.length > 0) {
8      var fileToLoad = filesSelected[0];
9
10      var fileReader = new FileReader();
11
12      fileReader.onload = function(fileLoadedEvent) {
13        var srcData = fileLoadedEvent.target.result; // <--- data: base64
14
15        var newImage = document.createElement('img');
16        newImage.src = srcData;
17
18        document.getElementById("imgTest").innerHTML = newImage.outerHTML;
19        alert("Converted Base64 version is " + document.getElementById("imgTest").innerHTML);
20        console.log("Converted Base64 version is " + document.getElementById("imgTest").innerHTML);
21      }
22      fileReader.readAsDataURL(fileToLoad);
23    }
24  }
25</script>