Question

我想为我的待办事项清单创建一个计数器。它显示所有项目的数量。但是当我添加项目时它不会更新。它保持在3。

这是我的Javascript代码；

var count = document.getElementById("list").childElementCount;
document.getElementById("title").innerHTML = ("You have " + count + " to-dos.");

// add item 
function todoList() {
    var item = document.getElementById("todoInput").value
    var text = document.createTextNode(item)
    var newItem = document.createElement("li")
    var check = document.createElement("span")
    check.className = "circle"
    newItem.appendChild(check)
    newItem.appendChild(text)
    document.getElementById("list").appendChild(newItem)

    // clear input value 
    document.getElementById("todoInput").value = "";
}

document.getElementById("add").addEventListener('click', todoList, null);

这是我的HTML代码；

<div class="progress">
    <div id="title"></div>
</div>

<ul id="list">
    <li><span class="circle"></span>Buid a task app</li>
    <li><span class="circle"></span>Do exercise</li>
    <li><span class="circle"></span>Buy headphones</li>
</ul>

Answer 1

只需在todoList()函数中重复子计数

 var count = document.getElementById("list").childElementCount;
  document.getElementById("title").innerHTML = ("You have " + count + " to-dos.");

// add item 
function todoList() {
  var item = document.getElementById("todoInput").value
  var text = document.createTextNode(item)
  var newItem = document.createElement("li")
  var check = document.createElement("span")
  check.className = "circle"
  newItem.appendChild(check)
  newItem.appendChild(text)
  document.getElementById("list").appendChild(newItem)


  count = document.getElementById("list").childElementCount;
  document.getElementById("title").innerHTML = ("You have " + count + " to-dos.");

  // clear input value 
  document.getElementById("todoInput").value = "";

}

document.getElementById("add").addEventListener('click', todoList, null);

或者您可以在javascript中阅读有关Getters and Setters的信息

Answer 2

DRY方法是创建一个可以调用的函数，因此您无需重复任何代码。

 new StaggeredGridLayoutManager(2, LinearLayoutManager.HORIZONTAL);

// Cache your elements
const title = document.getElementById('title');
const list = document.getElementById('list');
const input = document.getElementById('todoInput');
const add = document.getElementById('add')

// A new updateCount function
function updateCount() {
  const count = list.childElementCount;

  // Using a template literal is tidier than string concatenation
  // https://developer.mozilla.org/en/docs/Web/JavaScript/Reference/Template_literals
  title.innerHTML = `You have ${count} to-dos.`;
}

function todoList() {
  const item = input.value
  const text = document.createTextNode(item)
  const newItem = document.createElement('li')
  const check = document.createElement('span')
  check.className = 'circle'
  newItem.appendChild(check)
  newItem.appendChild(text)
  list.appendChild(newItem)
  input.value = '';

  // Call your updateCount function after a new item
  // has been added
  updateCount();
}

// Call updateCount initially when the page loads
updateCount();
add.addEventListener('click', todoList, false);

如何在Vanilla Javascript中计数列表中的项目？

2 个答案: