使用 useEffect 钩子停止反应导致无限循环

Question

I am very new to react and node, I have managed to create an API for a simple todo list. I have fetched the data from the api and presenting it on the screen.

If I leave the dependency array empty on the useEffect() hook it will only render once and doesn't loop. But If I add a new Todo it will not update the list unless I refresh. So I put the todos state into the dependency array, this will then show the new item when I add it but if I look at the network tab in the dev tools its hitting the api in an infinite loop. What am I doing wrong?

here is the code:

App

import React, { useState, useEffect } from "react";
import Todo from "./components/Todo";
import Heading from "./components/Heading";
import NewTodoForm from "./components/NewTodoForm";

const App = () => {
  const [todos, setTodos] = useState([]);

  useEffect(() => {
    const getTodos = async () => {
      const res = await fetch("http://localhost:3001/api/todos");
      const data = await res.json();
      setTodos(data);
    };

    getTodos();
  }, []);

  return (
    <div className="container">
      <Heading todos={todos} />
      <section className="todos-container">
        <ul className="todos">
          {todos.map((todo) => (
            <Todo key={todo._id} todo={todo} />
          ))}
        </ul>
      </section>
      <section className="todo-form">
        <NewTodoForm />
      </section>
    </div>
  );
};

export default App;

Heading

import React from "react";

const Heading = ({ todos }) => (
  <header>
    <h1>Todos</h1>
    <p>
      {todos.length} {todos.length === 1 ? "Item" : "Items"}
    </p>
  </header>
);

export default Heading;

Todo

import React, { useState } from "react";

const Todo = ({ todo }) => (
  <li>
    {todo.name}
    <input type="checkbox" />
  </li>
);

export default Todo;

NewTodoForm

import React, { useState } from "react";
import { Plus } from "react-feather";

const NewTodoForm = () => {
  const [formData, setFormData] = useState({
    name: "",
    completed: false,
  });

  const { name } = formData;

  const handleOnChange = (e) => {
    setFormData({
      ...formData,
      [e.target.name]: e.target.value,
    });
  };

  const handleSubmit = async (e) => {
    e.preventDefault();

    await fetch("http://localhost:3001/api/todos", {
      method: "POST",
      headers: {
        Accept: "application/json",
        "Content-Type": "application/json",
      },
      body: JSON.stringify(formData),
    });

    setFormData({
      name: "",
      completed: false,
    });
  };
  return (
    <form onSubmit={handleSubmit}>
      <div className="form-control">
        <Plus className="plus" />
        <input
          name="name"
          type="text"
          placeholder="Add New Item"
          onChange={handleOnChange}
          value={name}
        />
        <button>Add</button>
      </div>
    </form>
  );
};

export default NewTodoForm;

If I comment all the components out and only have the App component it still infinite loops when I add todos to the dependency array of the useEffect() hook.

Answer 1

So instead of giving that as a dependency write the function outside the useEffect so that you can call that function after you add a todo

Example:

  const getTodos = async () => {
      const res = await fetch("http://localhost:3001/api/todos");
      const data = await res.json();
      setTodos(data);
    };

 useEffect(() => {
    getTodos();
  }, []);

So getTodos will only run once initially and runs again only on the onSubmit or onClick of your Todo , So, just call getTodos function onSubmit or onClick