convert image url to base64 javascript

var xhr = new XMLHttpRequest();       
    xhr.open("GET", "/path/to/local/image/file", true); 
    xhr.responseType = "blob";
    xhr.onload = function (e) {
            console.log(this.response);
            var reader = new FileReader();
            reader.onload = function(event) {
               var res = event.target.result;
               console.log(res)
            }
            var file = this.response;
            reader.readAsDataURL(file)
    };
    xhr.send()var image = new Image();
image.src = 'data:image/png;base64,iVBORw0K...';
document.body.appendChild(image);function getBase64Image(src, callback, outputFormat) {
      const img = new Image();
      img.crossOrigin = 'Anonymous';
      img.onload = () => {
        const canvas = document.createElement('canvas');
        const ctx = canvas.getContext('2d');
        let dataURL;
        canvas.height = img.naturalHeight;
        canvas.width = img.naturalWidth;
        ctx.drawImage(img, 0, 0);
        dataURL = canvas.toDataURL(outputFormat);
        callback(dataURL);
      };

      img.src = src;
      if (img.complete || img.complete === undefined) {
        img.src = "data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///ywAAAAAAQABAAACAUwAOw==";
        img.src = src;
      }
    }function encodeImageFileAsURL(element) {
  var file = element.files[0];
  var reader = new FileReader();
  reader.onloadend = function() {
    console.log('RESULT', reader.result)
  }
  reader.readAsDataURL(file);
}
<input type="file" onchange="encodeImageFileAsURL(this)" />function getBase64Image(img) {
  var canvas = document.createElement("canvas");
  canvas.width = img.width;
  canvas.height = img.height;
  var ctx = canvas.getContext("2d");
  ctx.drawImage(img, 0, 0);
  var dataURL = canvas.toDataURL("image/png");
  return dataURL.replace(/^data:image\/(png|jpg);base64,/, "");
}

var base64 = getBase64Image(document.getElementById("imageid"));