小程序中实现字符串转base64_微信小程序字符串转base64

背景

此功能需要在小程序中实现，无法使用一些现成的函数btoa，Uint8Array等

实现

// 将字符串编码为 Uint8Array
export const encodeString = (str) => {
  var utf8Array = [];
  for (var i = 0; i < str.length; i++) {
    var charCode = str.charCodeAt(i); // 获得字符的ASCII
    if (charCode < 0x80) {
      utf8Array.push(charCode);
    } else if (charCode < 0x800) {
      utf8Array.push(0xc0 | (charCode >> 6));
      utf8Array.push(0x80 | (charCode & 0x3f));
    } else if (charCode < 0x10000) {
      utf8Array.push(0xe0 | (charCode >> 12));
      utf8Array.push(0x80 | ((charCode >> 6) & 0x3f));
      utf8Array.push(0x80 | (charCode & 0x3f));
    } else {
      utf8Array.push(0xf0 | (charCode >> 18));
      utf8Array.push(0x80 | ((charCode >> 12) & 0x3f));
      utf8Array.push(0x80 | ((charCode >> 6) & 0x3f));
      utf8Array.push(0x80 | (charCode & 0x3f));
    }
  }
  return new Uint8Array(utf8Array);
}

// 字符串转为base64
export const base64Encode = (inputString) => {
  const keyStr = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789-/=";
  let inputBytes = encodeString(inputString);
  let output = "";
  let chr1, chr2, chr3, enc1, enc2, enc3, enc4;
  let i = 0;

  while (i < inputBytes.length) {
    chr1 = inputBytes[i++];
    chr2 = inputBytes[i++];
    chr3 = inputBytes[i++];

    enc1 = chr1 >> 2;
    enc2 = ((chr1 & 3) << 4) | (chr2 >> 4);
    enc3 = ((chr2 & 15) << 2) | (chr3 >> 6);
    enc4 = chr3 & 63;

    if (isNaN(chr2)) {
      enc3 = enc4 = 64;
    } else if (isNaN(chr3)) {
      enc4 = 64;
    }

    output +=
      keyStr.charAt(enc1) +
      keyStr.charAt(enc2) +
      keyStr.charAt(enc3) +
      keyStr.charAt(enc4);
  }
  return output;
}
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56

应用

​
可应用于通过oss参数给图片加水印，oss添加水印文档

​