how img to base64 work code example

Example: how img to base64 work

/**
 * @param {Uint8Array} bytes
 * @return {string} Base64 encoded string
 */
function base64Encode(bytes) {
   let encoding = '';
   for (let group of groups24Bits(bytes)) {
      for (let value of values6Bits(group)) {
         if (value !== undefined) {
            encoding += ALPHABET[value];
         } else {
            encoding += PAD;
         }
      }
   }
   return encoding;
}

const ALPHABET = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/';
const PAD = '=';

/**
 * @param {Uint8Array} bytes
 * @return {Uint8Array} The next input group (yielded on each execution)
 */
function* groups24Bits(bytes) {
   for (let i = 0; i < bytes.length; i += 3) {
      yield bytes.slice(i, i + 3); // 3 bytes/3 octets/24 bits
   }
}

/**
 * @param {Uint8Array} group Expected to be array of 1 to 3 bytes
 * @return {number|undefined} The next 6-bit value from the 
 * input group (yielded on each execution)
 */
function* values6Bits(group) {
   const paddedGroup = Uint8Array.from([0, 0, 0]);
   paddedGroup.set(group);

   let numValues = Math.ceil((group.length * 8) / 6);
   for (let i = 0; i < numValues; i++) { let base64Value; if (i == 0) { base64Value = (paddedGroup[0] & 0b11111100) >> 2;
      } else if (i == 1) {
         base64Value = (paddedGroup[0] & 0b00000011) << 4; base64Value = base64Value | ((paddedGroup[1] & 0b11110000) >> 4);
      } else if (i == 2) {
         base64Value = (paddedGroup[1] & 0b00001111) << 2; base64Value = base64Value | ((paddedGroup[2] & 0b11000000) >> 6);
      } else if (i == 3) {
         base64Value = paddedGroup[2] & 0b00111111;
      }
      yield base64Value;
   }

   let numPaddingValues = 4 - numValues;
   for (let j = 0; j < numPaddingValues; j++) {
      yield undefined;
   }
}