使用 create-react-app 创建的脚手架项目，默认运行端口号是 3000，那我们该怎么修改这个默认的端口号呢？
{
"name": "react-demo",
"version": "0.1.0",
"private": true,
"dependencies": {
"@babel/core": "7.4.3",
"@svgr/webpack": "4.1.0",
"@typescript-eslint/eslint-plugin": "1.6.0",
"@typescript-eslint/parser": "1.6.0",
"antd": "^3.19.2",
"babel-eslint": "10.0.1",
"babel-jest": "^24.8.0",
"babel-loader": "8.0.5",
"babel-plugin-named-asset-import": "^0.3.2",
"babel-preset-react-app": "^9.0.0",
"camelcase": "^5.2.0",
"case-sensitive-paths-webpack-plugin": "2.2.0",
"css-loader": "2.1.1",
"dotenv": "6.2.0",
"dotenv-expand": "4.2.0",
"eslint": "^5.16.0",
"eslint-config-react-app": "^4.0.1",
"eslint-loader": "2.1.2",
"eslint-plugin-flowtype": "2.50.1",
"eslint-plugin-import": "2.16.0",
"eslint-plugin-jsx-a11y": "6.2.1",
"eslint-plugin-react": "7.12.4",
"eslint-plugin-react-hooks": "^1.5.0",
"file-loader": "3.0.1",
"fs-extra": "7.0.1",
"html-webpack-plugin": "4.0.0-beta.5",
"http-proxy-middleware": "^0.19.1",
"identity-obj-proxy": "3.0.0",
"is-wsl": "^1.1.0",
"jest": "24.7.1",
"jest-environment-jsdom-fourteen": "0.1.0",
"jest-resolve": "24.7.1",
"jest-watch-typeahead": "0.3.0",
"less": "^3.9.0",
"less-loader": "^5.0.0",
"mini-css-extract-plugin": "0.5.0",
"node": "^12.4.0",
"node-sass": "^4.12.0",
"optimize-css-assets-webpack-plugin": "5.0.1",
"pnp-webpack-plugin": "1.2.1",
"postcss-flexbugs-fixes": "4.1.0",
"postcss-loader": "3.0.0",
"postcss-normalize": "7.0.1",
"postcss-preset-env": "6.6.0",
"postcss-safe-parser": "4.0.1",
"react": "^16.8.6",
"react-app-polyfill": "^1.0.1",
"react-dev-utils": "^9.0.1",
"react-dom": "^16.8.6",
"react-router-dom": "^5.0.1",
"react-scripts": "^3.0.1",
"resolve": "1.10.0",
"semver": "6.0.0",
"style-loader": "0.23.1",
"terser-webpack-plugin": "1.2.3",
"ts-pnp": "1.1.2",
"url-loader": "1.1.2",
"webpack": "4.29.6",
"webpack-dev-server": "3.2.1",
"webpack-manifest-plugin": "2.0.4",
"workbox-webpack-plugin": "4.2.0"
},
"scripts": {
"start": "node scripts/start.js",
"build": "node scripts/build.js",
"test": "node scripts/test.js"
},
"eslintConfig": {
"extends": "react-app"
},
"browserslist": {
"production": [
">0.2%",
"not dead",
"not op_mini all"
],
"development": [
"last 1 chrome version",
"last 1 firefox version",
"last 1 safari version"
]
},
"jest": {
"collectCoverageFrom": [
"src/**/*.{js,jsx,ts,tsx}",
"!src/**/*.d.ts"
],
"setupFiles": [
"react-app-polyfill/jsdom"
],
"setupFilesAfterEnv": [],
"testMatch": [
"<rootDir>/src/**/__tests__/**/*.{js,jsx,ts,tsx}",
"<rootDir>/src/**/*.{spec,test}.{js,jsx,ts,tsx}"
],
"testEnvironment": "jest-environment-jsdom-fourteen",
"transform": {
"^.+\\.(js|jsx|ts|tsx)$": "<rootDir>/node_modules/babel-jest",
"^.+\\.css$": "<rootDir>/config/jest/cssTransform.js",
"^(?!.*\\.(js|jsx|ts|tsx|css|json)$)": "<rootDir>/config/jest/fileTransform.js"
},
"transformIgnorePatterns": [
"[/\\\\]node_modules[/\\\\].+\\.(js|jsx|ts|tsx)$",
"^.+\\.module\\.(css|sass|scss)$"
],
"modulePaths": [],
"moduleNameMapper": {
"^react-native$": "react-native-web",
"^.+\\.module\\.(css|sass|scss)$": "identity-obj-proxy"
},
"moduleFileExtensions": [
"web.js",
"js",
"web.ts",
"ts",
"web.tsx",
"tsx",
"json",
"web.jsx",
"jsx",
"node"
],
"watchPlugins": [
"jest-watch-typeahead/filename",
"jest-watch-typeahead/testname"
]
},
"babel": {
"presets": [
"react-app"
]
},
"devDependencies": {
"axios": "^0.19.0",
"gsap": "^2.1.3",
"sass": "^1.21.0",
"sass-loader": "^7.1.0"
}
}
从项目的 package.json 文件中可以看到，npm start即react-scripts start，它使用了 react-script 模块来启动项目。因此我们找到 /node_modules/react-scripts/scripts/start.js ，部分代码如下：
const openBrowser = require('react-dev-utils/openBrowser');
const paths = require('../config/paths');
const configFactory = require('../config/webpack.config');
const createDevServerConfig = require('../config/webpackDevServer.config');
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) || 3001;
const HOST = process.env.HOST || '0.0.0.0';
if (process.env.HOST) {
const DEFAULT_PORT = parseInt(process.env.PORT, 10) || 3001;
const HOST = process.env.HOST || '0.0.0.0';
找到 DEFAULT_PORT变量，修改它的默认值为 3001即可。
保存/node_modules/react-scripts/scripts/start.js 后，再执行npm start，即可看到项目在 3001端口上运行了。大功告成！
