React code debugging guide: How to quickly locate and solve front-end bugs

React Code Debugging Guide: How to quickly locate and solve front-end bugs

Introduction:
When developing React applications, you often encounter various bugs that may crash the application or cause incorrect behavior. Therefore, mastering debugging skills is an essential ability for every React developer. This article will introduce some practical techniques for locating and solving front-end bugs, and provide specific code examples to help readers quickly locate and solve bugs in React applications.

1. Selection of debugging tools:
In React applications, there are many tools that can help us debug the code. The following are several commonly used debugging tools:

1. Chrome Developer Tools: The developer tools that come with the Chrome browser are a powerful debugging tool that can inspect elements, view network requests, and view logs and other functions to debug React code.
2. React Developer Tools: This is a Chrome plug-in that provides more intuitive and detailed React component level information, as well as functions to help observe and modify the state of React components.
3. Redux DevTools: If your application uses Redux as a state management library, it is very helpful to use Redux DevTools to debug the Redux state flow. It can help you view and modify the status in the Redux store, as well as review historical status.

2. Locating React component exceptions:

1. Use the Elements panel of Chrome developer tools to check the React component hierarchy and see if the rendering results are as expected. You can determine the specific problem by checking component Props and state, and troubleshooting components that may be faulty.

Sample code:
Suppose we have a TodoList component that displays a to-do list.

import React, { useState } from 'react';

function TodoList() {
  const [todos, setTodos] = useState([]);

  function addTodo() {
    setTodos([...todos, { id: Date.now(), text: 'New todo' }]);
  }

  return (
    <div>
      <button onClick={addTodo}>Add Todo</button>
      {todos.map((todo) => (
        <div key={todo.id}>{todo.text}</div>
      ))}
    </div>
  );
}

export default TodoList;

Suppose an error is encountered when rendering the to-do list, and the corresponding rendering result cannot be displayed on the page. We can use the Elements panel of the Chrome developer tools to check whether there are rendering exceptions and see whether the status and Props are passed correctly.

2. Use the Console panel of Chrome Developer Tools to view warning and error messages in React components. React usually provides useful warning and error messages in development mode to help us locate specific problems.

Sample code:
Modify the TodoList component above to intentionally cause an error when rendering the to-do list.

import React, { useState } from 'react';

function TodoList() {
  const [todos, setTodos] = useState([]);

  function addTodo() {
    setTodos([...todos, { id: Date.now(), text: 'New todo' }]);
  }

  // 引发错误：todos.map is not a function
  const renderedTodos = todos.map((todo) => <div key={todo.id}>{todo.text}</div>);

  return (
    <div>
      <button onClick={addTodo}>Add Todo</button>
      {renderedTodos}
    </div>
  );
}

export default TodoList;

After refreshing the page, check the Console panel of Chrome developer tools and you can see the error message: todos.map is not a function. Through this error message, we can locate the location where the error occurred in the todos.map line of code.

3. Use breakpoint debugging:

1. In the Sources panel of Chrome developer tools, we can use the breakpoint debugging function to pause code execution on a certain line. At this time, we can view the value of the variable, call stack, execution context and other information to help us locate and solve the problem.

Sample code:
In the above TodoList component, we can set a breakpoint when clicking the button to add a to-do item.

import React, { useState } from 'react';

function TodoList() {
  const [todos, setTodos] = useState([]);

  function addTodo() {
    debugger; // 设置断点
    setTodos([...todos, { id: Date.now(), text: 'New todo' }]);
  }

  return (
    <div>
      <button onClick={addTodo}>Add Todo</button>
    </div>
  );
}

export default TodoList;

Refresh the page and open the Sources panel of Chrome Developer Tools, then click the button. The code will pause execution at the debugger line. At this time, we can view the code execution line by line and check whether the variable values ​​are correct.

2. In Redux development, you can use Redux DevTools to debug Redux state flow. Through Redux DevTools, we can view and modify the status in the Redux store, review historical status, and view the dispatch of Actions, etc.

Sample code:
If we have a Redux Store, it contains todos and filter states.

import { createStore } from 'redux';

const initialState = {
  todos: [],
  filter: 'all',
};

// 定义reducer函数
function reducer(state = initialState, action) {
  switch (action.type) {
    case 'ADD_TODO':
      return {
        ...state,
        todos: [...state.todos, action.payload],
      };
    case 'SET_FILTER':
      return {
        ...state,
        filter: action.payload,
      };
    default:
      return state;
  }
}

// 创建store
const store = createStore(reducer);

export default store;

We can use Redux DevTools to view and modify todos and filter status, as well as the execution of dispatched Actions.

Conclusion:
By using various debugging tools and techniques, we can quickly locate and solve front-end bugs. From checking the React component structure, viewing warning and error messages, to using breakpoint debugging and Redux DevTools, these methods can help us debug React code comprehensively and efficiently. Mastering these skills will significantly improve our efficiency and debugging capabilities in React development.

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