HTML5 Base64_encoding_and_decoding

https://developer.mozilla.org/en-US/docs/Web/API/WindowBase64/Base64_encoding_and_decoding

In JavaScript there are two functions respectively for decoding and encoding base64 strings:

• atob()
• btoa()

工作场景，客户端HTML片段的保存与再现。

The "Unicode Problem"

Since DOMStrings are 16-bit-encoded strings, in most browsers calling window.btoa on a Unicode string will cause a Character Out Of Range exception if a character exceeds the range of a 8-bit byte (0x00~0xFF). There are two possible methods to solve this problem:

• the first one is to escape the whole string (with UTF-8, see encodeURIComponent) and then encode it;
• the second one is to convert the UTF-16 DOMString to an UTF-8 array of characters and then encode it.

Here are the two possible methods.

https://developer.mozilla.org/en-US/docs/Web/API/WindowBase64/Base64_encoding_and_decoding#Solution_1_–_escaping_the_string_before_encoding_it

https://developer.mozilla.org/en-US/docs/Web/API/WindowBase64/Base64_encoding_and_decoding#Solution_2_–_rewrite_the_DOMs_atob()_and_btoa()_using_JavaScript's_TypedArrays_and_UTF-8

其它相关帖子：

https://blog.coding.net/blog/resolve-atob-decode-chinese-character-outputting-messy-code-problem-in-javascript

http://levy.work/2017-03-24-black-magic-js-atob-with-utf8/