如何查找和修复未定义属性的类型错误

Question

我正在学习关于填字游戏的教程，但是在我通过按键触发 selectLetter() 功能后，当我在 chrome 中运行它时收到此消息：

“未捕获的类型错误：无法读取未定义的属性'clueA'”*

当我在 Firefox 开发者中运行它时，这条消息：

“类型错误：currentLetter.dataset 未定义”。*

我尝试在 console.log 中使用 typeof 来跟踪 currentLetter 和 currentLetter.dataset 的值，但这让我更加困惑。

var allLetters;
var currentLetter;
var wordLetters;
var acrossClue;
var downClue;
var typeDirection = "right";
window.onload = init;

function init() {
  allLetters = document.querySelectorAll("table#crossword span");
  currentLetter = allLetters[0];
  var acrossID = currentLetter.dataset.clueA;
  var downID = currentLetter.dataset.clueD;
  acrossClue = document.getElementById(acrossID);
  downClue = document.getElementById(downID);
  formatPuzzle(currentLetter);
  for (var i = 0; i < allLetters.length; i++) {
    allLetters[i].style.cursor = "pointer";
    allLetters[i].onmousedown = function(e) {
      formatPuzzle(e.target);
    }
  }
  document.onkeydown = selectLetter;
  console.log("----init function----\n" + "Current Letter Type: " + typeof currentLetter + " \ncurrentLetter.dataset Type: " + typeof currentLetter.dataset);
}


function formatPuzzle(puzzleLetter) {
  currentLetter = puzzleLetter;
  for (var i = 0; i < allLetters.length; i++) {
    allLetters[i].style.backgroundColor = "";
  }
  acrossClue.style.color = "";
  downClue.style.color = "";

  if (currentLetter.dataset.clueA !== undefined) {
    acrossClue = document.getElementById(currentLetter.dataset.clueA);
    acrossClue.style.color = "blue";
    wordLetters = document.querySelectorAll("[data-clue-a=" + currentLetter.dataset.clueA + "]");
    for (i = 0; i < wordLetters.length; i++) {
      wordLetters[i].style.backgroundColor = "rgb(231,231,255)";
    }
  }
  if (currentLetter.dataset.clueD !== undefined) {
    downClue = document.getElementById(currentLetter.dataset.clueD);
    downClue.style.color = "red";
    wordLetters = document.querySelectorAll("[data-clue-d=" + currentLetter.dataset.clueD + "]");
    for (i = 0; i < wordLetters.length; i++) {
      wordLetters[i].style.backgroundColor = "rgb(255,231,231)";
    }
  }
  if (typeDirection === "right") {
    currentLetter.style.backgroundColor = "rgb(191,191,255)";
  } else {
    currentLetter.style.backgroundColor = "rgb(255,191,191)";
  }
  console.log("----formatPuzzle function----\n" + "Current Letter Type: " + typeof currentLetter + " \ncurrentLetter.dataset Type: " + typeof currentLetter.dataset);
}


function selectLetter(e) {
  var leftLetter = currentLetter.dataset.left;
  var upLetter = currentLetter.dataset.up;
  var rightLetter = currentLetter.dataset.right;
  var downLetter = currentLetter.dataset.down;
  var userKey = e.keyCode;
  console.log("----selectLetter function----\n" + "Current Letter Type: " + typeof currentLetter + " \ncurrentLetter.dataset Type: " + typeof currentLetter.dataset + "\n.dataset.up:" + currentLetter.dataset.up + "\nkeycode:" + userKey);
  if (userKey === 37) {
    formatPuzzle(leftLetter);
  } else if (userKey === 38) {
    formatPuzzle(upLetter);
  } else if (userKey === 39) {
    formatPuzzle(rightLetter);
  } else if ((userKey === 40) || (userKey === 13)) {
    formatPuzzle(downLetter);
  } else if ((userKey === 8) || (userKey === 46)) {
    currentLetter.textContent = "";
  } else if (userKey === 32) {
    switchTypeDirection;
  } else if (65 <= userKey <= 90) {
    currentLetter.textContent = getChar(userKey);
    if (typeDirection === "right") {
      formatPuzzle(rightLetter);
    } else {
      formatPuzzle(downLetter);
    }
  }
  e.preventDefault();
}

function switchTypeDirection() {

}

function getChar(keyNum) {
  return String.fromCharCode(keyNum);
}

<table id="crossword">
  <caption>Today's Crossword</caption>
  <tr>
    <td><span id="c1_1" data-letter="C" data-right="c1_2" data-left="c1_8" data-down="c2_1" data-up="c11_1" data-clue-a="a1" data-clue-d="d1"></span><sup>1</sup></td>
    <td><span id="c1_2" data-letter="A" data-right="c1_3" data-left="c1_1" data-down="c2_2" data-up="c11_2" data-clue-a="a1" data-clue-d="d2"></span><sup>2</sup></td>
    <td><span id="c1_3" data-letter="M" data-right="c1_4" data-left="c1_2" data-down="c2_3" data-up="c11_3" data-clue-a="a1" data-clue-d="d3"></span><sup>3</sup></td>
    <td><span id="c1_4" data-letter="O" data-right="c1_5" data-left="c1_3" data-down="c2_4" data-up="c10_4" data-clue-a="a1" data-clue-d="d4"></span><sup>4</sup></td>
    <td><span id="c1_5" data-letter="M" data-right="c1_6" data-left="c1_4" data-down="c2_5" data-up="c11_5" data-clue-a="a1" data-clue-d="d5"></span><sup>5</sup></td>
    <td><span id="c1_6" data-letter="I" data-right="c1_7" data-left="c1_5" data-down="c2_6" data-up="c11_6" data-clue-a="a1" data-clue-d="d6"></span><sup>6</sup></td>
    <td><span id="c1_7" data-letter="L" data-right="c1_8" data-left="c1_6" data-down="c2_7" data-up="c11_7" data-clue-a="a1" data-clue-d="d7"></span><sup>7</sup></td>
    <td><span id="c1_8" data-letter="E" data-right="c1_1" data-left="c1_7" data-down="c2_8" data-up="c11_8" data-clue-a="a1" data-clue-d="d8"></span><sup>8</sup></td>
    <td class="blank"></td>
  </tr>

我希望箭头键可以更改拼图中箭头键指向的单元格的背景颜色 rgb(191,191,255)，但代码停止运行，并且控制台会打印类型错误。

Answer 1

该错误意味着currentLetter 被分配了一个不是DOM 元素的值（因为每个DOM 元素都有一个dataset 属性）。

您分配给currentLetter 的唯一位置是init：

currentLetter = allLetters[0];

和formatPuzzle:

currentLetter = puzzleLetter;

allLetters[0] 将是一个 DOM 元素。

puzzleLetter 是formatPuzzle 的参数，所以让我们看看函数是否被调用并传递了不是 DOM 元素的东西。

在selectLetter 中，您使用不同的参数多次调用formatPuzzle，但它们都不是DOM 元素。例如。 leftLetter 是currentLetter.dataset.left 的值。

也许你打算这样做

var leftLetter = documnent.getElementById(currentLetter.dataset.left);
// etc

?

---

确保只将 DOM 元素传递给函数，并尽可能避免使用全局变量。