使用方法window.btoa 將字符串轉為base64編碼
使用方法window.atob 將base64編碼轉為js字符串
var string = “Hello World”
let base64 = window.btoa(string)
let str = window.atob(base64)
注意：
javascript中的字符的實現一般是16位無符號整數
（http://www.ecma-international.org/ecma-262/5.1/#sec-15.5.1）
window.btoa接收的string是8位的，所以，如果是超過8位的，比如unicode編碼 中的中文就會報錯
(
- btoa() accepts a “string” where each character represents an 8-bit byte – if you pass a string containing characters that can’t be represented in 8 bits, it willprobablybreak. This isn’t a problem if you’re actually treating the string as a byte array, but if you’re trying to do something else then you’ll have to encode it first.
- atob() returns a “string” where each character represents an 8-bit byte – that is, its value will be between 0 and 0xff. This does not mean it’s ASCII – presumably if you’re using this function at all, you expect to be working with binary data and not text.
)
let str = ‘我叫’
window.btoa(str) // InvalidCharacterError: String contains an invalid character
可以先將unicode text轉換為utf-8編碼（encodeURIComponent），然后使用base64編碼，解碼的時候再轉換回來,就能得到原先的text
注意：
encodeURIComponent的轉義范圍比encodeURI更大