我如何将本地存储用于待办事项列表？

3回答

qq_花开花谢_0

本地存储将 JSON 对象保存到用户的计算机。您应该创建一个待办事项数组，将该数组附加到每个新待办事项中，然后将该项目设置为本地存储。let ul = document.querySelector('ul');const savedTodos = JSON.parse(localStorage.getItem("todos")) || []; // Retrieves local storage todo OR creates empty array if none existlet newItem = document.querySelector('input[type=text]');let checkbox = document.createElement('input');checkbox.setAttribute('type', 'checkbox');function output() {    let newTodo = document.createElement('li');    newTodo.innerText = newItem.value;    newTodo.classList.add('todo');    ul.append(newTodo);    newTodo.append(checkbox);    savedTodos.push({task: newItem.value, isCompleted: false}); // Appends the new todo to array    localStorage.setItem("todos", JSON.stringify(savedTodos)); //Converts object to string and stores in local storage    newItem.value = '';}

0 0

九州编程

我已经用一些评论对您发布的解决方案进行了注释，以帮助您逐步完成它。// Retrieve elements and store them in variablesconst todoForm = document.getElementById("newTodoForm");const todoList = document.getElementById("todoList");// Get data stored in localStorage under the key "todos".// The data type will be a string (local storage can only store strings).// JSON is a global object that contains methods for working with data represented as strings.// The `||` syntax is an OR operator and is used here to set an empty array as a fallback in case `localStorage` is emptyconst savedTodos = JSON.parse(localStorage.getItem("todos")) || [];// Create a loop the same length as the list of todosfor (let i = 0; i < savedTodos.length; i++) {  // Create an <li> element in memory (does not appear in the document yet)  let newTodo = document.createElement("li");  // Set the inner text of that new li with the contents from local storage.  // The savedTodos[i] is accessing data in the localStorage array.  // The [i] is a different number each loop.  // The `.task` is accessing 'task' property on the object in the array.  newTodo.innerText = savedTodos[i].task;  // Create a new property on the element called `isCompleted` and assign a boolean value.  // This is only accessible in code and will not show up when appending to the DOM.  newTodo.isCompleted = savedTodos[i].isCompleted ? true : false;  // Check the value we just set.  if (newTodo.isCompleted) {    // Create a style for the element if it is done (strike it out)    newTodo.style.textDecoration = "line-through";  }  // Actually append the new element to the document (this will make it visible)  todoList.appendChild(newTodo);}// `addEventListener` is a function that registers some actions to take when an event occurs.// The following tells the browser - whenever a form is submitted, run this function.todoForm.addEventListener("submit", function(event) {  // Don't try to send the form data to a server. Stops page reloading.  event.preventDefault();  // Create a <li> element in memory (not yet visible in the document)  let newTodo = document.createElement("li");  // Find element in the document (probably a input element?) and access the text value.  let taskValue = document.getElementById("task").value;  // Set the text of the <li>  newTodo.innerText = taskValue;  // Set a property on the <li> call `isCompleted`  newTodo.isCompleted = false;  // Empty out all the input fields in the form  todoForm.reset();  // Make the new <li> visible in the document by attaching it to the list  todoList.appendChild(newTodo);  // `push` adds a new element to the `savedTodos` array. In this case, an object with 2 properties.  savedTodos.push({ task: newTodo.innerText, isCompleted: false });  // Overwrite the `todos` key in local storage with the updated array.  // Use the JSON global object to turn an array into a string version of the data  // eg [1,2,3] becomes "[1,2,3]"  localStorage.setItem("todos", JSON.stringify(savedTodos));});// This tells the browser - whenever the todoList is clicked, run this function.// The browser will call the your function with an object that has data about the event.todoList.addEventListener("click", function(event) {  // the `target` of the event is the element that was clicked.  let clickedListItem = event.target;  // If that element has a property called `isCompleted` set to true  if (!clickedListItem.isCompleted) {    // update the styles and toggle the `isCompleted` property.    clickedListItem.style.textDecoration = "line-through";    clickedListItem.isCompleted = true;  } else {    clickedListItem.style.textDecoration = "none";    clickedListItem.isCompleted = false;  }  // The code above changes the documents version of the data (the elements themselves)  // This loop ensures that the array of todos data is kept in sync with the document  // Loop over the array  for (let i = 0; i < savedTodos.length; i++) {    // if the item in the array has the same text as the item just clicked...    if (savedTodos[i].task === clickedListItem.innerText) {      // toggle the completed state      savedTodos[i].isCompleted = clickedListItem.isCompleted;      // Update the localStorage with the new todos array.      localStorage.setItem("todos", JSON.stringify(savedTodos));    }  }});请记住，您的待办事项列表中有 2 个状态来源。一个是文档的外观，另一个是todos数据数组。许多挑战来自确保这两个保持同步。如果文档以某种方式显示其中一个列表项被划掉，但您的数据数组显示所有todos未完成，那么哪个版本是正确的？这里没有正确的答案，但状态管理将是您未来设计应用程序时可能会考虑的问题。Redux是一个很好的 js 库，具有很好理解的模式，可以帮助解决这个问题。希望这最后的评论不会混淆太多。祝你好运！

0 0

温温酱

重要的部分是（反）序列化数据。这意味着：localStorage从( JSON.parse(localStorage.getItem("todos")) || [])读取我们添加默认值[]，因为如果todos键不存在，我们将得到null并且我们期望一个列表保存到localStorage( localStorage.setItem("todos", JSON.stringify(savedTodos)))我们需要JSON.parse和它的补充操作JSON.stringify来解析和保存字符串，因为 localStorage 只能存储字符串。在您的情况下，您需要从 localStorage 读取数据并呈现初始列表。要将其保存到 localStorage，您必须再次序列化数据。请参阅下面的片段（链接到工作JSFIDDLE，因为下面的示例在 StackOverflow 沙箱环境中不起作用）：let ul = document.querySelector('ul');let newItem = document.querySelector('input[type=text]');const Store = {  serialize () {    return [].slice.call(document.querySelectorAll("li")).map(c => {      return {        text: c.textContent,        finished: c.querySelector("input").checked      }    })  },  get () {    return JSON.parse(localStorage.getItem("todos")) || []  },  save () {    return localStorage.setItem("todos", JSON.stringify(Store.serialize()))  }}const firstItems = Store.get()firstItems.forEach(it => {  output(it.text, it.finished)})function output(v, finished) {  let newTodo = document.createElement('li');  newTodo.innerText = v || newItem.value;  newTodo.classList.add('todo');  let ulAppend = ul.append(newTodo);  ul.append(newTodo);  // Create a checkbox for each item  let checkbox = document.createElement('input');  if (finished) {    checkbox.checked = true  }  checkbox.setAttribute('type', 'checkbox');  let checkboxAppend = newTodo.append(checkbox);  newTodo.append(checkbox);  newItem.value = '';}let button = document.querySelector('.btn');button.addEventListener('click', () => {    output()  Store.save()});ul.addEventListener('click', function(e) {  if (e.target.tagName === 'LI') {    e.target.remove();  } else if (e.target.tagName === 'INPUT') {    e.target.parentElement.classList.toggle('finished');  }  // Update the value in localStorage when you delete or add a new item  Store.save()});<ul></ul><input type="text" /> <button class="btn">Submit</button>我添加了Store变量以简化您在 localStorage 中获取和设置数据的方式。serialize 方法将从列表中读取 TODO。document.querySelectorAll("li")返回 a NodeList，但通过这样做[].slice.call(...)我们将其转换为 a Array。

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