react-create-app项目解析一 start.js
知识准备：
| const WebpackDevServer = require('webpack-dev-server'); | 利用 webpack-dev-server 主要提供两个功能 1 为静态文件提供服务 2 自动刷新和热替换（HMR |
主要是下面这段代码，通过WebpackDevServer来开启一个服务。
if (port == null) {
// We have not found a port.
return;
}
const config = configFactory("development");
const protocol = process.env.HTTPS === "true" ? "https" : "http";
const appName = require(paths.appPackageJson).name;
const useTypeScript = fs.existsSync(paths.appTsConfig);
const tscCompileOnError = process.env.TSC_COMPILE_ON_ERROR === "true";
const urls = prepareUrls(
protocol,
HOST,
port,
paths.publicUrlOrPath.slice(0, -1)
);
const devSocket = {
warnings: (warnings) =>
devServer.sockWrite(devServer.sockets, "warnings", warnings),
errors: (errors) =>
devServer.sockWrite(devServer.sockets, "errors", errors),
};
// Create a webpack compiler that is configured with custom messages.
const compiler = createCompiler({
appName,
config,
devSocket,
urls,
useYarn,
useTypeScript,
tscCompileOnError,
webpack,
});
// Load proxy config
const proxySetting = require(paths.appPackageJson).proxy;
const proxyConfig = prepareProxy(
proxySetting,
paths.appPublic,
paths.publicUrlOrPath
);
// Serve webpack assets generated by the compiler over a web server.
const serverConfig = createDevServerConfig(
proxyConfig,
urls.lanUrlForConfig
);
const devServer = new WebpackDevServer(compiler, serverConfig);
// Launch WebpackDevServer.
devServer.listen(port, HOST, (err) => {
if (err) {
return console.log(err);
}
if (isInteractive) {
clearConsole();
}
if (env.raw.FAST_REFRESH && semver.lt(react.version, "16.10.0")) {
console.log(
chalk.yellow(
`Fast Refresh requires React 16.10 or higher. You are using React ${react.version}.`
)
);
}
console.log(chalk.cyan("Starting the development server...\n"));
openBrowser(urls.localUrlForBrowser);
});
["SIGINT", "SIGTERM"].forEach(function (sig) {
process.on(sig, function () {
devServer.close();
process.exit();
});
});
if (process.env.CI !== "true") {
// Gracefully exit when stdin ends
process.stdin.on("end", function () {
devServer.close();
process.exit();
});
}| if (port == null) { // We have not found a port. return; } | 如果不存在端口，直接返回 |
| const config = configFactory("development"); | webpack配置对象 |
| const protocol = process.env.HTTPS === "true" ? "https" : "http"; | 使用协议 |
| const useTypeScript = fs.existsSync(paths.appTsConfig); | 根目录下是否存在tsconfig.json配置文件 |
| const tscCompileOnError = process.env.TSC_COMPILE_ON_ERROR === "true"; | 编译是否出现错误 |
| const urls = prepareUrls( protocol, HOST, port, paths.publicUrlOrPath.slice(0, -1) ); | WebpackDevServer访问地址 |
| const devSocket = { warnings: (warnings) => devServer.sockWrite(devServer.sockets, "warnings", warnings), errors: (errors) => devServer.sockWrite(devServer.sockets, "errors", errors), }; | |
| // Create a webpack compiler that is configured with custom messages. const compiler = createCompiler({ appName, config, devSocket, urls, useYarn, useTypeScript, tscCompileOnError, webpack, }); | |
| // Load proxy config const proxySetting = require(paths.appPackageJson).proxy; | |
| const proxyConfig = prepareProxy( proxySetting, paths.appPublic, paths.publicUrlOrPath ); | |
| // Serve webpack assets generated by the compiler over a web server. const serverConfig = createDevServerConfig( proxyConfig, urls.lanUrlForConfig ); | |
| const devServer = new WebpackDevServer(compiler, serverConfig); | |
| // Launch WebpackDevServer. devServer.listen(port, HOST, (err) => { if (err) { return console.log(err); } if (isInteractive) { clearConsole(); } if (env.raw.FAST_REFRESH && semver.lt(react.version, "16.10.0")) { console.log( chalk.yellow( `Fast Refresh requires React 16.10 or higher. You are using React ${react.version}.` ) ); } console.log(chalk.cyan("Starting the development server...\n")); openBrowser(urls.localUrlForBrowser); }); | 启动WebpackDevServer， devServer.listen已经废弃，应该使用startCallback。 openBrowser(urls.localUrlForBrowser);打开浏览器 |
| ["SIGINT", "SIGTERM"].forEach(function (sig) { process.on(sig, function () { devServer.close(); process.exit(); }); }); if (process.env.CI !== "true") { // Gracefully exit when stdin ends process.stdin.on("end", function () { devServer.close(); process.exit(); }); } | 首先要知道的是SIGINT、SIGKILL和SIGTERM代表的时一种信号。什么是信号？信号是一个 POSIX 内部通信系统：发送通知给进程，以告知其发生的事件。（windows系统不支持）。 这三个个信号都是用来终止进程的。 三者之间的区别 kill -2 <process_id> kill <process_id> kill -9 <process_id> process.stdin 标准输入流 （终端键盘输入） |
const devServer = new WebpackDevServer(compiler, serverConfig);
compiler：webpack执行对象
serverConfig：WebpackDevServer配置对象，包含服务器地址，端口等等。
总结：
react-create-app通过 Node.js API 使用 dev-server，则webpack.config.js中 devServer 的配置选项将被忽略。并不是直接执行webpack命令。
TODO。。。。。后续再核验完善
源码
'use strict';
// Do this as the first thing so that any code reading it knows the right env.
process.env.BABEL_ENV = 'development';
process.env.NODE_ENV = 'development';
// Makes the script crash on unhandled rejections instead of silently
// ignoring them. In the future, promise rejections that are not handled will
// terminate the Node.js process with a non-zero exit code.
process.on('unhandledRejection', err => {
throw err;
});
// Ensure environment variables are read.
require('../config/env');
const fs = require('fs');
const chalk = require('react-dev-utils/chalk');
const webpack = require('webpack');
const WebpackDevServer = require('webpack-dev-server');
const clearConsole = require('react-dev-utils/clearConsole');
const checkRequiredFiles = require('react-dev-utils/checkRequiredFiles');
const {
choosePort,
createCompiler,
prepareProxy,
prepareUrls,
} = require('react-dev-utils/WebpackDevServerUtils');
const openBrowser = require('react-dev-utils/openBrowser');
const semver = require('semver');
const paths = require('../config/paths');
const configFactory = require('../config/webpack.config');
const createDevServerConfig = require('../config/webpackDevServer.config');
const getClientEnvironment = require('../config/env');
const react = require(require.resolve('react', { paths: [paths.appPath] }));
const env = getClientEnvironment(paths.publicUrlOrPath.slice(0, -1));
const useYarn = fs.existsSync(paths.yarnLockFile);
const isInteractive = process.stdout.isTTY;
// Warn and crash if required files are missing
if (!checkRequiredFiles([paths.appHtml, paths.appIndexJs])) {
process.exit(1);
}
// Tools like Cloud9 rely on this.
const DEFAULT_PORT = parseInt(process.env.PORT, 10) || 3000;
const HOST = process.env.HOST || '0.0.0.0';
if (process.env.HOST) {
console.log(
chalk.cyan(
`Attempting to bind to HOST environment variable: ${chalk.yellow(
chalk.bold(process.env.HOST)
)}`
)
);
console.log(
`If this was unintentional, check that you haven't mistakenly set it in your shell.`
);
console.log(
`Learn more here: ${chalk.yellow('https://cra.link/advanced-config')}`
);
console.log();
}
// We require that you explicitly set browsers and do not fall back to
// browserslist defaults.
const { checkBrowsers } = require('react-dev-utils/browsersHelper');
checkBrowsers(paths.appPath, isInteractive)
.then(() => {
// We attempt to use the default port but if it is busy, we offer the user to
// run on a different port. `choosePort()` Promise resolves to the next free port.
return choosePort(HOST, DEFAULT_PORT);
})
.then(port => {
if (port == null) {
// We have not found a port.
return;
}
const config = configFactory('development');
const protocol = process.env.HTTPS === 'true' ? 'https' : 'http';
const appName = require(paths.appPackageJson).name;
const useTypeScript = fs.existsSync(paths.appTsConfig);
const tscCompileOnError = process.env.TSC_COMPILE_ON_ERROR === 'true';
const urls = prepareUrls(
protocol,
HOST,
port,
paths.publicUrlOrPath.slice(0, -1)
);
const devSocket = {
warnings: warnings =>
devServer.sockWrite(devServer.sockets, 'warnings', warnings),
errors: errors =>
devServer.sockWrite(devServer.sockets, 'errors', errors),
};
// Create a webpack compiler that is configured with custom messages.
const compiler = createCompiler({
appName,
config,
devSocket,
urls,
useYarn,
useTypeScript,
tscCompileOnError,
webpack,
});
// Load proxy config
const proxySetting = require(paths.appPackageJson).proxy;
const proxyConfig = prepareProxy(
proxySetting,
paths.appPublic,
paths.publicUrlOrPath
);
// Serve webpack assets generated by the compiler over a web server.
const serverConfig = createDevServerConfig(
proxyConfig,
urls.lanUrlForConfig
);
const devServer = new WebpackDevServer(compiler, serverConfig);
// Launch WebpackDevServer.
devServer.listen(port, HOST, err => {
if (err) {
return console.log(err);
}
if (isInteractive) {
clearConsole();
}
if (env.raw.FAST_REFRESH && semver.lt(react.version, '16.10.0')) {
console.log(
chalk.yellow(
`Fast Refresh requires React 16.10 or higher. You are using React ${react.version}.`
)
);
}
console.log(chalk.cyan('Starting the development server...\n'));
openBrowser(urls.localUrlForBrowser);
});
['SIGINT', 'SIGTERM'].forEach(function (sig) {
process.on(sig, function () {
devServer.close();
process.exit();
});
});
if (process.env.CI !== 'true') {
// Gracefully exit when stdin ends
process.stdin.on('end', function () {
devServer.close();
process.exit();
});
}
})
.catch(err => {
if (err && err.message) {
console.log(err.message);
}
process.exit(1);
});