React | 修改React脚手架的默认端口号？

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！

本文章来自https://www.jianshu.com/p/eb78e2fc9571