Convert Image To Base64 in TypeScript with comments for better explanation

ImageBlobUtil.ts

/**
 * further explanation on promise, resolve and reject can be found here: `https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise/Promise`
 * further explanation on FileReader can be found here: `https://developer.mozilla.org/en-US/docs/Web/API/FileReader`
 */

// the funciton accepts a paramerter of type File, and a promise to define return type
export const ImageToBase64 = (file: File): Promise<string> => {
  // define a reader of type FileReader
  const reader = new FileReader();
  //
  return new Promise((resolve, reject) => {
    reader.readAsDataURL(file); // Start reading the file passed as a parameter

    // define event listeners to track reader upon completion or error
    // `onloadend` event is triggered when reading operation is completed
    reader.onloadend = () => {
      // check that reader has a result
      if (reader.result) {
        // resolve promise with the result
        resolve(reader.result.toString());
      } else {
        // reject the promise with a new error (you can do some another action here)
        reject(new Error("error reading file"));
      }
    };
    // `onerror` event is triggered upon error reading file
    reader.onerror = () => {
      reject(new Error("Error reading file")); // also reject the promise with a new error
    };
  });
};