小程序实现base64编解码

• string和arrayBuffer互相转换 

  arrayBuffer2String(arr) {
    if (typeof arr === 'string') {
      return arr;
    }
    var tmparr = new Uint8Array(arr);
    var str = '';
    for (var i = 0; i < tmparr.length; i++) {
      var one = tmparr[i].toString(2);
      var v = one.match(/^1+?(?=0)/);
      if (v && one.length == 8) {
        var bytesLength = v[0].length;
        var store = tmparr[i].toString(2).slice(7 - bytesLength);
        for (var st = 1; st < bytesLength; st++) {
          store += tmparr[st + i].toString(2).slice(2);
        }
        str += String.fromCharCode(parseInt(store, 2));
        i += bytesLength - 1;
      } else {
        str += String.fromCharCode(tmparr[i]);
      }
    }
    return str;
  },

  string2ArrayBuffer(str) {
    var bytes = new Array();
    var len, c;
    len = str.length;
    for (var i = 0; i < len; i++) {
      c = str.charCodeAt(i);
      if (c >= 0x010000 && c <= 0x10FFFF) {
        bytes.push(((c >> 18) & 0x07) | 0xF0);
        bytes.push(((c >> 12) & 0x3F) | 0x80);
        bytes.push(((c >> 6) & 0x3F) | 0x80);
        bytes.push((c & 0x3F) | 0x80);
      } else if (c >= 0x000800 && c <= 0x00FFFF) {
        bytes.push(((c >> 12) & 0x0F) | 0xE0);
        bytes.push(((c >> 6) & 0x3F) | 0x80);
        bytes.push((c & 0x3F) | 0x80);
      } else if (c >= 0x000080 && c <= 0x0007FF) {
        bytes.push(((c >> 6) & 0x1F) | 0xC0);
        bytes.push((c & 0x3F) | 0x80);
      } else {
        bytes.push(c & 0xFF);
      }
    }
    var array = new Int8Array(bytes);
    return array.buffer;
  },

• base64编码

let arrayBuffer = this.string2ArrayBuffer(string)
let base64 = wx.arrayBufferToBase64(arrayBuffer)

• base64解码

let arrayBuffer = wx.base64ToArrayBuffer(base64)
let string = this.arrayBuffer2String(arrayBuffer)