您可以更有效地迭代单词，但这非常简单：

function secretCipher(sentence, cipher){
 return sentence.split('').map(letter => cipher[letter] ?? letter).join('');
}


//Uncomment the lines below to test your function:

console.log(secretCipher("lqq me on flcebzzk" , { l : "a", q : "d", z: "o"})); //=> "add me on        facebook"
console.log(secretCipher("where are you???" , { v : "l", '?' : "!"})) //=> "where are you!!!"
console.log(secretCipher("twmce" , { m : "n", t : "d", w : "a"})); //=> "dance"

如果您的浏览器不知道??是什么，请将其替换为||。根据MDN，它应该可以在所有现代浏览器上工作。

• let value = cipher[key];什么也不做，因为value没有在其他任何地方被引用（它的作用域在循环迭代结束后结束）
• if (sentence[i].includes(cyf)) {没有意义，因为sentence[i]是字符串（字符），而cyf是键数组。字符串不包含数组。请检查数组是否包含字符。
• sentence[i] = sentence[i].replace(sentence[i], value)不起作用，因为字符串是不可变的。请创建一个新字符串。
• 当找到匹配时，添加原始的sentence[i]没有意义-您希望用对象上的值替换，而不是用原始字符替换。

function secretCipher(sentence, cipher) {
  let result = '';
  const keys = Object.keys(cipher);
  // iterate through sentence, if char in string is stricktly equal to the key
  for (let i = 0; i < sentence.length; i++) {
    if (keys.includes(sentence[i])) {
      result += cipher[sentence[i]];
    } else {
      result += sentence[i]
    }
  }
  return result;
}

console.log(secretCipher("lqq me on flcebzzk", {
  l: "a",
  q: "d",
  z: "o"
})); //=> "add me on        facebook"
console.log(secretCipher("where are you???", {
  v: "l",
  '?': "!"
})) //=> "where are you!!!"
console.log(secretCipher("twmce", {
  m: "n",
  t: "d",
  w: "a"
})); //=> "dance"

或者更准确地说

function secretCipher(sentence, cipher) {
  let result = '';
  for (const char of sentence) {
    result += cipher[char] ?? char;
  }
  return result;
}

console.log(secretCipher("lqq me on flcebzzk", {
  l: "a",
  q: "d",
  z: "o"
})); //=> "add me on        facebook"
console.log(secretCipher("where are you???", {
  v: "l",
  '?': "!"
})) //=> "where are you!!!"
console.log(secretCipher("twmce", {
  m: "n",
  t: "d",
  w: "a"
})); //=> "dance"