学习使用JavaScript实现UTF-8编解码

function utf8Decode(inputStr) {

  var outputStr = "";

  var code1, code2, code3, code4;

  for(var i = 0; i < inputStr.length; i++) {

    code1 = inputStr.charCodeAt(i);

    if(code1 < 128) {

      outputStr += String.fromCharCode(code1);

    }

    else if(code1 < 224) {

      code2 = inputStr.charCodeAt(++i);

      outputStr += String.fromCharCode(((code1 & 31) << 6) | (code2 & 63));

    }

    else if(code1 < 240) {

      code2 = inputStr.charCodeAt(++i);

      code3 = inputStr.charCodeAt(++i);

      outputStr += String.fromCharCode(((code1 & 15) << 12) | ((code2 & 63) << 6) | (code3 & 63));

    }

    else {

      code2 = inputStr.charCodeAt(++i);

      code3 = inputStr.charCodeAt(++i);

      code4 = inputStr.charCodeAt(++i);

      outputStr += String.fromCharCode(((code1 & 7) << 18) | ((code2 & 63) << 12) |((code3 & 63) << 6) | (code2 & 63));

    }

  }

  return outputStr;

}