React调试——visual studio code

原文链接：Using React in Visual Studio Code

原文链接:Live edit and debug your React apps directly from VS Code — without leaving the editor

github源码示例：microsoft/vscode-react-sample

Welcome to React

you'll need Node.js JavaScript runtime and npm (Node.js package manager) installed. npm is included with Node.js which you can download and install from Node.js downloads.

Tip: To test that you have Node.js and npm correctly installed on your machine, you can type node --version and npm --version in a terminal or command prompt.

 using the create-react-app generator for this tutorial

To install the create-react-app generator, in a terminal or command prompt type:

npm install -g create-react-app

This may take a few minutes to install. You can now create a new React application by typing:

create-react-app my-app

where my-app is the name of the folder for your application. This may take a few minutes to create the React application and install its dependencies.

Let's quickly run our React application by navigating to the new folder and typing npm start to start the web server and open the application in a browser:

cd my-app
npm start

You should see the React logo and a link to "Learn React" on http://localhost:3000 in your browser. We'll leave the web server running while we look at the application with VS Code.

To open your React application in VS Code, open another terminal or command prompt window, navigate to the my-app folder and type code .:

cd my-app
code .

Markdown preview

In the File Explorer, one file you'll see is the application README.md Markdown file. This has lots of great information about the application and React in general. 

A nice way to review the README is by using the VS Code Markdown Preview. You can open the preview in either the current editor group (Markdown: Open Preview Ctrl+Shift+V) or in a new editor group to the side (Markdown: Open Preview to the Side Ctrl+K V). You'll get nice formatting, hyperlink navigation to headers, and syntax highlighting in code blocks.

Syntax highlighting and bracket matching

Now expand the src folder and select the index.js file. You'll notice that VS Code has syntax highlighting for the various source code elements and, if you put the cursor on a parenthesis, the matching bracket is also selected.

After you select a suggestion and type ., you see the types and methods on the object through IntelliSense.

……

Debugging React

To debug the client side React code, we'll need to install the Debugger for Chromeextension.

Note: This tutorial assumes you have the Chrome browser installed. Microsoft also publishes a version of this extension for their Edge browser.

……

Configure the Chrome debugger

We need to initially configure the debugger. To do so, go to the Debug view (Ctrl+Shift+D) and click on the gear button to create a launch.json debugger configuration file. Choose Chrome from the Select Environment drop-down list. This will create a launch.json file in a new .vscode folder in your project which includes a configuration to launch the website.

We need to make one change for our example: change the port of the url from 8080to 3000. Your launch.json should look like this:

{
  "version": "0.2.0",
  "configurations": [
    {
      "type": "chrome",
      "request": "launch",
      "name": "Launch Chrome against localhost",
      "url": "http://localhost:3000",
      "webRoot": "${workspaceFolder}"
    }
  ]
}

　

……

Live editing and debugging

If you are using webpack together with your React app, you can have a more efficient workflow by taking advantage of webpack's HMR mechanism which enables you to have live editing and debugging directly from VS Code. You can learn more in this Live edit and debug your React apps directly from VS Code blog post and the webpack Hot Module Replacement documentation.

Linting

Linters analyze your source code and can warn you about potential problems before you run your application. The JavaScript language services included with VS Code has syntax error checking support by default which you can see in action in the Problemspanel (View > Problems Ctrl+Shift+M).

Try making a small error in your React source code and you'll see a red squiggle and an error in the Problems panel.

Linters can provide more sophisticated analysis, enforcing coding conventions and detecting anti-patterns. A popular JavaScript linter is ESLint. ESLint, when combined with the ESLint VS Code extension, provides a great in-product linting experience.

First, install the ESLint command-line tool:

npm install -g eslint

Then install the ESLint extension by going to the Extensions view and typing 'eslint'.

 Once the ESLint extension is installed and VS Code reloaded, you'll want to create an ESLint configuration file .eslintrc.json. You can create one using the extension's ESLint: Create ESLint configuration command from the Command Palette(Ctrl+Shift+P).

 The command will create a .eslintrc.json file in your project root:

{
  "env": {
    "browser": true,
    "commonjs": true,
    "es6": true,
    "node": true
  },
  "parserOptions": {
    "ecmaFeatures": {
      "jsx": true
    },
    "sourceType": "module"
  },
  "rules": {
    "no-const-assign": "warn",
    "no-this-before-super": "warn",
    "no-undef": "warn",
    "no-unreachable": "warn",
    "no-unused-vars": "warn",
    "constructor-super": "warn",
    "valid-typeof": "warn"
  }
}

　　

ESLint will now analyze open files and shows a warning in index.js about 'App' being defined but never used.

 

You can modify the ESLint rules and the ESLint extension provides IntelliSense in .eslintrc.json.

Let's add an error rule for extra semi-colons:

 "rules": {
        "no-const-assign": "warn",
        "no-this-before-super": "warn",
        "no-undef": "warn",
        "no-unreachable": "warn",
        "no-unused-vars": "warn",
        "constructor-super": "warn",
        "valid-typeof": "warn",
        "no-extra-semi":"error"
    }

　Now when you mistakenly have multiple semicolons on a line, you'll see an error (red squiggle) in the editor and error entry in the Problems panel.　

Popular Starter Kits

In this tutorial, we used the create-react-app generator to create a simple React application. There are lots of great samples and starter kits available to help build your first React application

VS Code React Sample

This is a sample React application used for a demo at this year's //Build conference. The sample creates a simple TODO application and includes the source code for a Node.js Express server. It also shows how to use the Babel ES6 transpiler and then use webpackto bundle the site assets

MERN Starter

If you'd like to see a full MERN (MongoDB, Express, React, Node.js) stack example, look at the MERN Starter. You'll need to install and start MongoDB but you'll quickly have a MERN application running. There is helpful VS Code-specific documentation at vscode-recipes which details setting up Node.js server debugging. VS Code also has great MongoDB support through the Azure Cosmos DB extension

TypeScript React

If you're curious about TypeScript and React, you can also create a TypeScript version of the create-react-app application. See the details at TypeScript-React-Starter on the TypeScript Quick Start site.

Angular

Angular is another popular web framework. If you'd like to see an example of Angular working with VS Code, check out the Chrome Debugging with Angular CLI recipe. It will walk you through creating an Angular application and configuring the launch.jsonfile for the Debugger for Chrome extensio

　

Common questions

Can I get IntelliSense within declarative JSX?

Yes. For example, if you open the create-react-app project's App.js file, you can see IntelliSense within the React JSX in the render() method.

In our most recent release of our Chrome debugger for VS Code, we have landed a bunch of improvements to our sourcemapping-engine, which enables us to support live-editing and debugging out of the box with create-react-app.

This enables you as a developer to write and debug your React code without leaving the editor, and most importantly it enables you to have a continuous development workflow, where context switching is minimal, as you don’t have to switch between tools.

 You can now write code, set a breakpoints, make a changes to the code, and debug your newly modified code — all from your editor

How to get started in 6 steps

1. Download the latest release of VS Code and install our Chrome debugger
2. Create your React app using create-react-app
3. Use the following config for your launch.jsonfile to configure the VS Code debugger and put it inside .vscode in your root folder.

{
    "version": "0.2.0",
    "configurations": [
        {
            "name": "Chrome",
            "type": "chrome",
            "request": "launch",
            "url": "http://localhost:3000",
            "webRoot": "${workspaceRoot}/src"
        }
    ]
}

4. Start your React app by running npm start in your favorite terminal

5. Start debugging in VS Code by pressing F5or by clicking the green debug icon

Happy debugging! 

　　

Details

Our Chrome debugger now supports Webpack’s Hot Module Replacement mechanism, which pushes module changes to the browser by running a local file watcher.

Our debugger is now able to pickup these changes and re-applies the newly generated HMR sourcemap to the loaded source files on the fly. This enables the live editing and debugging experiences, without adding a need for more file watches or background tools.