How to convert base 64 to byte Array?

Question

How to convert base64 to byte Array in angular. I am trying it but it doesn't work.

// file upload
 handleUpload(event) {
   if (event.target.files[0]) {
     this.file = event.target.files[0].name;
   }
   const file = event.target.files[0];
   const reader = new FileReader();
   reader.readAsDataURL(file);
   reader.onload = () => {
     // console.log(reader.result);
     this.base64ToArrayBuffer(reader.result);
   };
 }

  //  base64  to byte array
  base64ToArrayBuffer(base64) {
    var binary_string = window.atob(base64)
    var len = binary_string.length;
    var bytes = new Uint8Array(len);
    for (var i = 0; i < len; i++) {
      bytes[i] = binary_string.charCodeAt(i);
    }
    console.log(bytes.buffer)
    this.fileBase64 = bytes.buffer;
    return bytes.buffer;
  }

I want to fileBase64 variable to be a byte Array but it doesn't work.