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[英]SyntaxError Unexpected token < in JSON at position 0 in react.js API navigation
[英]Unexpected token u in JSON at position 0 in React.js todo app after deployment on netlify
我正在嘗試在 netlify 上部署 react 應用程序。 在本地,我的 react todo 應用程序運行良好,並且本地存儲也在(本地)保存數據。 但是當我在 netlify 上部署 Web 應用程序時,在訪問實時鏈接后,它向我顯示了這個錯誤:“JSON.parse 中位置 0 處的 JSON 中的意外令牌 u”,因為它正在檢索未定義的內容。 我嘗試過的解決方案:檢查錯字 2:檢查控制台中正確顯示數據的對象。 3:我還在 App() 函數中保留了 getTodoFromLocal 函數,並保留了 const [todos, setTodos] = useState([]); 的初始狀態。 (到空數組)但這不是在頁面重新加載時保留數據
我的代碼App.js
import React, {useEffect, useState} from 'react';
import './App.css';
import { Header, Form, TodoList } from './components';
// get data from local
const getTodoFromLocal = () => {
if(localStorage.getItem("todos") === null){
localStorage.setItem("todos", JSON.stringify([]));
} else {
try{
let localTodo = localStorage.getItem("todos");
let parsedTodo = JSON.parse(localTodo)
return parsedTodo;
} catch(error) {
console.log(error);
}
}
}
const App = () => {
// states
const [inputText, setInputText] = useState("");
const [todos, setTodos] = useState(getTodoFromLocal());
const [status, setStatus] = useState("all");
const [filteredTodo, setFilteredTodo] = useState([]);
// run this only once when app loads
useEffect(() => {
getTodoFromLocal();
}, [])
// Run once when app loads and every time when there is any change in todos ot status
useEffect(() => {
filterHandler();
saveToLocal();
}, [todos, status])
// functions
const filterHandler = () =>{
switch (status) {
case 'completed':
setFilteredTodo(todos.filter(todo => todo.completed === true));
break;
case 'incompleted':
setFilteredTodo(todos.filter(todo => todo.completed === false));
break;
default:
setFilteredTodo(todos);
break;
}
}
// save to local storage / set todos;
const saveToLocal = () => {
localStorage.setItem("todos", JSON.stringify(todos));
};
return (
<div className="App">
<Header />
<Form inputText = {inputText}
setInputText={setInputText}
todos={todos}
setTodos={setTodos}
setStatus={setStatus}
/>
<TodoList
todos={todos}
setTodos={setTodos}
filteredTodo={filteredTodo}
/>
</div>
);
}
export default App;
TodoList.js
import React from 'react';
import TodoItem from './TodoItem';
const TodoList = ({todos, setTodos, filteredTodo}) => {
return (
<div className='todo-container'>
<ul className='todo-list'>
{filteredTodo && filteredTodo.map(todo => (
<TodoItem
key={todo.id}
todo={todo}
todos={todos}
setTodos={setTodos}
text={todo.text}
/>
))}
</ul>
</div>
)
}
export default TodoList;
表單.js
import React from 'react';
import './form.css';
import { v4 as uuidv4 } from 'uuid';
function Form({inputText, setInputText, todos, setTodos, setStatus}) {
const inputHandler = (e) => {
setInputText(e.target.value);
}
const submitHandler = (e) =>{
e.preventDefault();
// generate unique id for todo lists.
const uniqueId = uuidv4();
//add todo object on click of button
const addItem = !inputText ? alert("enter somthing") : setTodos([
...todos, {id: uniqueId, text: inputText, completed: false }
]);
//reset the input field after adding todo
setInputText("");
return addItem;
}
// filtered todo
const statusTodo = (e) => {
setStatus(e.target.value);
}
return (
<form>
<input type="text" className="todo-input" onChange={inputHandler} value={inputText}/>
<button className="todo-button" type="submit" onClick={submitHandler}>
<i className="fas fa-plus-square"></i>
</button>
<div className="select">
<select onChange={statusTodo} name="todos" className="filter-todo">
<option value="all">All</option>
<option value="completed">Completed</option>
<option value="incompleted">Incompleted</option>
</select>
<span><i className="fas fa-chevron-down"></i></span>
</div>
</form>
)
}
export default Form;
TodoItem.js
import React from 'react';
import './todo.css';
const TodoItem = ({text, todo, todos, setTodos}) => {
//delete an item;
const deleteHandler = () => {
setTodos(todos.filter(el => el.id !== todo.id))
}
const completeHandler = () => {
setTodos(todos.map((item )=> {
if(item.id === todo.id){
return {
...item, completed: !todo.completed
}
}
return item;
}));
}
return (
<div className='todo'>
<li className={`todo-item ${todo.completed ? 'completed' : "" }`}>{text}</li>
<button className='complete-btn' onClick={completeHandler}>
<i className='fas fa-check'></i>
</button>
<button className='trash-btn' onClick={deleteHandler}>
<i className='fas fa-trash'></i>
</button>
</div>
)
}
export default TodoItem;
直播鏈接: https ://clinquant-parfait-ceab31.netlify.app/
Github 鏈接: https ://github.com/Mehreen57/Todo-app-react
我想出了錯誤。 一步一步走。
你有getTodoFromLocal
,當你 setTodos const [todos, setTodos] = useState(getTodoFromLocal());
這里。
由於localStorage.getItem("todos")
為空,您將todos
設置為[]
但不返回任何返回 undefined 的內容,並且 todos 的值更改為undefined
。
然后你就有了saveToLocal
函數,你可以在其中將todos
存儲在localStorage
中。每當 todos 發生變化時,就會在 useEffect 中調用它。
Todos 更改為undefined
> useEffect 被調用 > 在saveToLocal
函數中 todos(undefined) 存儲在 localStorage 中。
更新代碼:
if (localStorage.getItem("todos") === null) {
localStorage.setItem("todos", JSON.stringify([]));
return []
}
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