React Hook“useState”在函数“app”中调用，它既不是React函数组件，也不是自定义React Hook函数

我试图使用反应钩子来解决一个简单的问题

const [personState,setPersonState] = useState({ DefinedObject });

具有以下依赖关系。

"dependencies": {
    "react": "^16.8.6",
    "react-dom": "^16.8.6",
    "react-scripts": "3.0.0"
}

但我仍然得到以下错误:

/ src / App.js 第7行: React钩子useState在函数中被调用 “app”既不是React函数组件，也不是自定义React 钩子函数react-hooks/rules-of-hooks 39行: 'state'没有定义 no-undef 搜索关键字以了解关于每个错误的更多信息。

组件代码如下:

import React, {useState} from 'react'; 
import './App.css'; 
import Person from './Person/Person'; 

const app = props => { 
    const [personState, setPersonSate] = useState({ person:[ {name:'bishnu',age:'32'}, {name:'rasmi',age:'27'}, {name:'fretbox',age:'4'} ], }); 
    return (
        <div className="App"> 
            <h2>This is react</h2> 
            <Person name={personState.person[1].name} age="27"></Person>
            <Person name={personState.person[2].name} age="4"></Person> 
        </div> ); 
    };
    export default app;

人组件

import React from 'react'; 

const person = props => { 
    return( 
        <div>
            <h3>i am {props.name}</h3>
            <p>i am {props.age} years old</p>
            <p>{props.children}</p>
        </div> 
    )
};

export default person;

当前回答

可能是在没有条件的useEffect之前添加了依赖于条件的useEffect

EX:

useEffect(() => {
  _anyFunction();
}, []);
    
useEffect(()=> {
  anyCode....
}, [response]);

2021-02-13 12:55:46

其他回答

用户定义的组件必须大写。在你的例子中，你使用了const app = props =>{}。在“app”中，“a”是小写的，你必须尝试使用“app”

When an element type starts with a lowercase letter, it refers to a built-in component like <div> or <span> and results in a string 'div' or 'span' passed to React.createElement. Types that start with a capital letter like <Foo /> compile to React.createElement(Foo) and correspond to a component defined or imported in your JavaScript file. React recommend naming components with a capital letter. If you do have a component that starts with a lowercase letter, assign it to a capitalized variable before using it in JSX.

更多详情请查阅官方文件点击这里

2022-11-30 05:28:58

使用const App而不是const App

2020-03-09 06:45:02

你的代码

import React, {useState} from 'react'; 
import './App.css'; 
import Person from './Person/Person'; 

const app = props => { 
    const [personState, setPersonSate] = useState({ person:[ {name:'bishnu',age:'32'}, {name:'rasmi',age:'27'}, {name:'fretbox',age:'4'} ], }); 
    return (
        <div className="App"> 
            <h2>This is react</h2> 
            <Person name={personState.person[1].name} age="27"></Person>
            <Person name={personState.person[2].name} age="4"></Person> 
        </div> ); 
    };
    export default app;

将函数名改为大写，就像这样

import React, {useState} from 'react'; 
import './App.css'; 
import Person from './Person/Person'; 

const App = props => { 
    const [personState, setPersonSate] = useState({ person:[ {name:'bishnu',age:'32'}, {name:'rasmi',age:'27'}, {name:'fretbox',age:'4'} ], }); 
    return (
        <div className="App"> 
            <h2>This is react</h2> 
            <Person name={personState.person[1].name} age="27"></Person>
            <Person name={personState.person[2].name} age="4"></Person> 
        </div> ); 
    };
    export default App;

会有用的谢谢。

2021-05-01 02:35:21

函数的第一个字符应该是大写的

2020-02-24 15:15:35

不要使用箭头函数创建功能组件。

按照下面的例子做:

function MyComponent(props) {
  const [states, setStates] = React.useState({ value: '' });

  return (
    <input
      type="text"
      value={states.value}
      onChange={(event) => setStates({ value: event.target.value })}
    />
  );
}

//IMPORTANT: Repeat the function name

const MyComponent = function MyComponent(props) { 
  const [states, setStates] = React.useState({ value: '' });

  return (
    <input
      type="text"
      value={states.value}
      onChange={(event) => setStates({ value: event.target.value })}
    />
  );
};

如果你有“ref”的问题(可能在循环中)，解决方案是使用forwardRef():

// IMPORTANT: Repeat the function name
// Add the "ref" argument to the function, in case you need to use it.

const MyComponent = React.forwardRef( function MyComponent(props, ref) {
  const [states, setStates] = React.useState({ value: '' });

  return (
    <input
      type="text"
      value={states.value}
      onChange={(event) => setStates({ value: event.target.value })}
    />
  );
});

2020-01-29 22:58:58

React Hook“useState”在函数“app”中调用，它既不是React函数组件，也不是自定义React Hook函数

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