JavaScript动态创建对象未定义

Question

我正在做 freecodecamp 算法挑战赛“Caesars Cipher”。我的代码有问题。我尝试生成一个查找表作为动态对象，但由于某种原因它没有注册。当执行 console.log 时，它显示“查找表未定义”。 Acode 变量也是如此。如果我注释掉 console.logs 那么它会工作，但它不会加密任何东西，因为下面的部分检查 strArr 中的字符是否存在于 LookupTable 中，如果不存在，它应该为 cryptoArr 分配相同的值(这是已完成，不加密逗号、空格等):

strArr.forEach(function(thisArg) {
    var newValue;

    if(lookupTable[thisArg] !== undefined ) {
      newValue = lookupTable[thisArg];
    } else {
      newValue = thisArg;
    }

    encryptedArr.push(newValue);

});

当然lookupTable[thisArg]始终是未定义的。这是包含上述部分的整个函数:

function rot13(str) { // LBH QVQ VG!

  var strArr;
  var encryptedArr = [];
  var Acode;
  var lookupTable = {}; //this object will contain the mapping of letters
  var encryptedString;

  //check the code of A , this will be a reference for the first letter as the algorith will use Modular Arithmetic
  Acode = 'A'.charCodeAt(0);
  console.log(Acode);
  //generate an object containing mappings (I din't want to do it initially but theoreticaly just making lookups in a table would be more efficiant for huge workloads than calculating it every time)
  //this algorithm is a little bit complecated but i don't know how to do modular arithmetic in code properly so I use workarrounds. If a = 101 then I do 101 + the remainder from current letter((Acode + 1) - 13) divided by 26  which works

  for (i = 0; i < 26; i++) {
    lookupTable[String.fromCharCode(Acode + i)] = String.fromCharCode(Acode + ((Acode + i) - 13) % 26);
    console.log(lookupTable[String.fromCharCode(Acode + i)]);
  }

  //save the string into the array
  strArr = str.split("");

  //change letters into numbers and save into the code array
  strArr.forEach(function(thisArg) {
    var newValue;

    if (lookupTable[thisArg] !== undefined) {
      newValue = lookupTable[thisArg];
    } else {
      newValue = thisArg;
    }

    encryptedArr.push(newValue);

  });


  encryptedString = encryptedArr.join("");


  return encryptedString;
}

// Change the inputs below to test
rot13("SERR PBQR PNZC");
console.log(Acode);

我在创建lookupTable对象和下面的内容时做错了什么？

  Acode = 'A'.charCodeAt(0);

Answer 1

没有 undefined variable 。您的代码的问题在于如何计算查找表条目。您的代码将每个字符映射到其自身，而不是移动 13。正确的公式是

Acode + ((i + 13) % 26)

Acode 是字母的 ASCII 代码，在执行模数转换时不应包含该代码。您只想将模数应用于从字母表开头偏移 13 后的偏移量。

function rot13(str) { // LBH QVQ VG!

  var strArr;
  var encryptedArr = [];
  var Acode;
  var lookupTable = {}; //this object will contain the mapping of letters
  var encryptedString;

  //check the code of A , this will be a reference for the first letter as the algorith will use Modular Arithmetic
  Acode = 'A'.charCodeAt(0);
  // console.log(Acode);
  //generate an object containing mappings (I din't want to do it initially but theoreticaly just making lookups in a table would be more efficiant for huge workloads than calculating it every time)
  //this algorithm is a little bit complecated but i don't know how to do modular arithmetic in code properly so I use workarrounds. If a = 101 then I do 101 + the remainder from current letter((Acode + 1) - 13) divided by 26  which works

  for (i = 0; i < 26; i++) {
    lookupTable[String.fromCharCode(Acode + i)] = String.fromCharCode(Acode + ((i + 13) % 26));
    // console.log(lookupTable[String.fromCharCode(Acode + i)]);
  }

  //save the string into the array
  strArr = str.split("");

  //change letters into numbers and save into the code array
  strArr.forEach(function(thisArg) {
    var newValue;

    if (lookupTable[thisArg] !== undefined) {
      newValue = lookupTable[thisArg];
    } else {
      newValue = thisArg;
    }

    encryptedArr.push(newValue);

  });


  encryptedString = encryptedArr.join("");


  return encryptedString;
}

// Change the inputs below to test
var result = rot13("SERR PBQR PNZC");
console.log(result);