Source: utils/b64.js

/**
 * @see https://github.com/englercj/resource-loader/blob/v2.1.1/src/b64.js
 */

const _keyStr = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/=';

/**
 *
 * @param {string} input
 * @return {string}
 */
export function encodeBinary(input) {
  let output = '';
  let inx = 0;

  while (inx < input.length) {
    // Fill byte buffer array
    const bytebuffer = [0, 0, 0];
    const encodedCharIndexes = [0, 0, 0, 0];

    for (let jnx = 0; jnx < bytebuffer.length; ++jnx) {
      if (inx < input.length) {
        // throw away high-order byte, as documented at:
        // https://developer.mozilla.org/En/Using_XMLHttpRequest#Handling_binary_data
        bytebuffer[jnx] = input.charCodeAt(inx++) & 0xff;
      } else {
        bytebuffer[jnx] = 0;
      }
    }

    // Get each encoded character, 6 bits at a time
    // index 1: first 6 bits
    encodedCharIndexes[0] = bytebuffer[0] >> 2;

    // index 2: second 6 bits (2 least significant bits from input byte 1 + 4 most significant bits from byte 2)
    encodedCharIndexes[1] = ((bytebuffer[0] & 0x3) << 4) | (bytebuffer[1] >> 4);

    // index 3: third 6 bits (4 least significant bits from input byte 2 + 2 most significant bits from byte 3)
    encodedCharIndexes[2] = ((bytebuffer[1] & 0x0f) << 2) | (bytebuffer[2] >> 6);

    // index 3: forth 6 bits (6 least significant bits from input byte 3)
    encodedCharIndexes[3] = bytebuffer[2] & 0x3f;

    // Determine whether padding happened, and adjust accordingly
    const paddingBytes = inx - (input.length - 1);

    switch (paddingBytes) {
      case 2:
        // Set last 2 characters to padding char
        encodedCharIndexes[3] = 64;
        encodedCharIndexes[2] = 64;
        break;
      case 1:
        // Set last character to padding char
        encodedCharIndexes[3] = 64;
        break;
      default:
        break; // No padding - proceed
    }

    // Now we will grab each appropriate character out of our keystring
    // based on our index array and append it to the output string
    for (let jnx = 0; jnx < encodedCharIndexes.length; ++jnx) {
      output += _keyStr.charAt(encodedCharIndexes[jnx]);
    }
  }

  return output;
}