client-mime-check.js

import * as fileType from 'file-type';
const MIN_FILE_SIZE = 0;
const MAX_FILE_SIZE = Number.MAX_SAFE_INTEGER;
const ALLOWED_FILE_MIMETYPES: string[] = [];

function validateFileSize(file: File): boolean {
  return file.size >= MIN_FILE_SIZE && file.size <= MAX_FILE_SIZE;
}

function validateFileMimetype(file: File): Promise<boolean> {
  return new Promise((resolve, reject) => {
    const blob = file.slice(0, fileType.minimumBytes);
    const reader = new FileReader();
    reader.onloadend = (e) => {
      if (e.target.readyState !== FileReader.DONE) {
        reject("Error validating mime");
      }
      const bytes = new Uint8Array(e.target.result);
      const { ext, mime } = fileType.fromBuffer(bytes);
      console.log("Validating file:", ext, mime);
      resolve(ALLOWED_FILE_MIMETYPES.includes(mime));
    };
    reader.readAsArrayBuffer(blob);
  });
}

export async function validateFile(file: File): Promise<boolean> {
  return validateFileSize(file) && (await validateFileMimetype(file));
}