在微信小程序中使用 btoa、atob 函数

前言

在某些场景下，我们经常需要创建一个 base-64 编码的字符串，在 js 中可以直接使用 window.btoa() 方法来实现，但是在微信小程序中并没有 window 对象，所以可以自己实现一个 btoa() 方法。

实现

btoa

"use strict";
Object.defineProperty(exports, "__esModule", { value: true });
var b64 = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/=";
var b64re =
  /^(?:[A-Za-z\d+\/]{4})*?(?:[A-Za-z\d+\/]{2}(?:==)?|[A-Za-z\d+\/]{3}=?)?$/;
exports.mpBtoa = function (string) {
  string = String(string);
  var bitmap,
    a,
    b,
    c,
    result = "",
    i = 0,
    rest = string.length % 3;
  for (; i < string.length; ) {
    if (
      (a = string.charCodeAt(i++)) > 255 ||
      (b = string.charCodeAt(i++)) > 255 ||
      (c = string.charCodeAt(i++)) > 255
    )
      throw new TypeError(
        "Failed to execute 'btoa' on 'Window': The string to be encoded contains characters outside of the Latin1 range."
      );
    bitmap = (a << 16) | (b << 8) | c;
    result +=
      b64.charAt((bitmap >> 18) & 63) +
      b64.charAt((bitmap >> 12) & 63) +
      b64.charAt((bitmap >> 6) & 63) +
      b64.charAt(bitmap & 63);
  }
  return rest ? result.slice(0, rest - 3) + "===".substring(rest) : result;
};

atob

"use strict";
exports.mpAtob = function (string) {
  string = String(string).replace(/[\t\n\f\r ]+/g, "");
  if (!b64re.test(string))
    throw new TypeError(
      "Failed to execute 'atob' on 'Window': The string to be decoded is not correctly encoded."
    );
  string += "==".slice(2 - (string.length & 3));
  var bitmap,
    result = "",
    r1,
    r2,
    i = 0;
  for (; i < string.length; ) {
    bitmap =
      (b64.indexOf(string.charAt(i++)) << 18) |
      (b64.indexOf(string.charAt(i++)) << 12) |
      ((r1 = b64.indexOf(string.charAt(i++))) << 6) |
      (r2 = b64.indexOf(string.charAt(i++)));
    result +=
      r1 === 64
        ? String.fromCharCode((bitmap >> 16) & 255)
        : r2 === 64
        ? String.fromCharCode((bitmap >> 16) & 255, (bitmap >> 8) & 255)
        : String.fromCharCode(
            (bitmap >> 16) & 255,
            (bitmap >> 8) & 255,
            bitmap & 255
          );
  }
  return result;
};

小程序中使用

1. 新建 mp.js 文件，新增函数 mpBtoa、mpAtob github
2. 引入

   import { mpBtoa, mpAtob } from "./mp.js";