Get Base64 File Size

get-base64-file-size.js

const base64 =
  "data:image/png;base64,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";

function getBase64FileSize(base64) {
  const base64str = base64.substring(base64.indexOf(",") + 1);
  const decoded = atob(base64str);
  const bytes = decoded.length;
  const kb = bytes / 1024;

  return {
    fileSize: Math.round(kb) + "KB",
    bytes: bytes / 1000,
  };
}

console.log(getBase64FileSize(base64)); // { fileSize: '3KB', bytes: 2.652 }