image-js/src/util/base64.js

Image processing and manipulation in JavaScript

/*
 * base64-arraybuffer
 * https://github.com/niklasvh/base64-arraybuffer
 *
 * Copyright (c) 2012 Niklas von Hertzen
 * Licensed under the MIT license.
 */

let chars = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/';

// Use a lookup table to find the index.
let lookup = new Uint8Array(256);
for (let i = 0; i < chars.length; i++) {
  lookup[chars.charCodeAt(i)] = i;
}

export function encode(bytes) {
  let i;
  let len = bytes.length;
  let base64 = '';

  for (i = 0; i < len; i += 3) {
    base64 += chars[bytes[i] >> 2];
    base64 += chars[((bytes[i] & 3) << 4) | (bytes[i + 1] >> 4)];
    base64 += chars[((bytes[i + 1] & 15) << 2) | (bytes[i + 2] >> 6)];
    base64 += chars[bytes[i + 2] & 63];
  }

  if (len % 3 === 2) {
    base64 = `${base64.substring(0, base64.length - 1)}=`;
  } else if (len % 3 === 1) {
    base64 = `${base64.substring(0, base64.length - 2)}==`;
  }

  return base64;
}

export function decode(base64) {
  let bufferLength = base64.length * 0.75;
  let len = base64.length;
  let p = 0;
  let encoded1, encoded2, encoded3, encoded4;

  if (base64[base64.length - 1] === '=') {
    bufferLength--;
    if (base64[base64.length - 2] === '=') {
      bufferLength--;
    }
  }

  const bytes = new Uint8Array(bufferLength);

  for (let i = 0; i < len; i += 4) {
    encoded1 = lookup[base64.charCodeAt(i)];
    encoded2 = lookup[base64.charCodeAt(i + 1)];
    encoded3 = lookup[base64.charCodeAt(i + 2)];
    encoded4 = lookup[base64.charCodeAt(i + 3)];

    bytes[p++] = (encoded1 << 2) | (encoded2 >> 4);
    bytes[p++] = ((encoded2 & 15) << 4) | (encoded3 >> 2);
    bytes[p++] = ((encoded3 & 3) << 6) | (encoded4 & 63);
  }

  return bytes;
}

export function toBase64URL(u8, type) {
  const base64 = encode(u8);
  return `data:${type};base64,${base64}`;
}