Question

此“计数器”的目标是查看“ ToCount”字符串中有多少个不同的单词。为此，它使ToCount成为数组，然后遍历元素，检查它们是否已经存在，如果不存在，则将它们添加到那里。

在循环后，ToCountArr2保持为空，并且显示长度为0。为什么会发生这种情况，我该怎么办？

我运行了一个调试器，发现没有元素添加到第二个列表中，好像如果第一个数组的第i个元素已经在第二个数组中，则“ if”控件中没有任何内容。

function counter(){
    var ToCount = document.getElementById("demo").value; //the contents of a textbox
    var ToCountArr1 = ToCount.split(" ");
    var ToCountArr2 = new Array;
    var i = 0;
    var lengthToCountArr1 = ToCountArr1.length;
    var wordToPush;
    while (i < lengthToCountArr1){
    if(ToCountArr2.includes(ToCountArr1[i] === false)) {
            wordToPush = ToCountArr1[i];
            ToCountArr2.push(wordToPush);
        }
        i = i + 1;
    }
    alert(ToCountArr2.length);
}

Answer 1

问题在于此行if(ToCountArr2.includes(ToCountArr1[i] === false))。在这里，花括号必须位于ToCountArr1[i]之后，ToCountArr1[i] === false)这行正在检查ToCountArr1中的值是true还是false。

此行

if(ToCountArr2.includes(ToCountArr1[i] === false))将被评估为

if(ToCountArr2.includes(true/false)) 取决于ToCountArr1[i] === false)

的结果

function counter() {
  var ToCount = document.getElementById("demo").value; //the contents of a textbox
  var ToCountArr1 = ToCount.split(" ");
  var ToCountArr2 = new Array;
  var i = 0;
  var lengthToCountArr1 = ToCountArr1.length;
  var wordToPush;

  while (i < lengthToCountArr1) {
    if (ToCountArr2.includes(ToCountArr1[i]) === false) {
      wordToPush = ToCountArr1[i];
      ToCountArr2.push(wordToPush);
    }
    i = i + 1;
  }
  console.log(ToCountArr2.length);
}

counter()

<input type='text' id='demo' value='Test Values'>

您可以通过将

替换为if (ToCountArr2.includes(ToCountArr1[i]) === false) {来使其最小化

if (!ToCountArr2.includes(ToCountArr1[i])) {

Answer 2

您的wordcount函数应使用一个参数，以便您可以传递一个字符串。这意味着您可以在任意字符串上使用wordcount函数，而不仅仅是“演示”元素。另外，这是学习Map-

的好时机

const wordcount = (str = "") =>
{ const result =
    new Map
  
  for (const s of str.split(/ /))
    if (s === "")
      continue
    else if (result.has(s))
      result.set(s, result.get(s) + 1)
    else
      result.set(s, 1)
  
  return Array.from(result.entries())
}

const prettyPrint = (value) =>
  console.log(JSON.stringify(value))

<!-- pass this.value as the string for wordcount
  -- wordcount returns a value that we could use elsewhere
  -- prettyPrint displays the value to the console
  -->
<input onkeyup="prettyPrint(wordcount(this.value))">

运行代码段并将以下行复制/粘贴到字段中-

this is the captain speaking. is this the commander?

您将看到此输出-

[["this",2],["is",2],["the",2],["captain",1],["speaking.",1],["commander?",1]]

Answer 3

这是一个有效的示例。我认为这会帮助您正确的方法。在这里，我使用indexOf来检查数组中是否存在该值。

function counter(){
    var ToCount = "I am string just for text.";//document.getElementById("demo").value; //the contents of a textbox
    var ToCountArr1 = ToCount.split(" ");
    var ToCountArr2 = new Array;
    var i = 0;
    var lengthToCountArr1 = ToCountArr1.length;
    var wordToPush;
    while (i < lengthToCountArr1){
    if( ToCountArr2.indexOf(ToCountArr1[i]) == -1 ) {
            wordToPush = ToCountArr1[i];
            ToCountArr2.push(wordToPush);
        }
        i = i + 1;
    }
    alert(ToCountArr2.length);
}
counter();

为什么第二个数组保持为空？

3 个答案: