start.js

/* eslint-disable no-magic-numbers, unicorn/no-process-exit, no-console, prefer-template */
// 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 { checkBrowsers } = require("react-dev-utils/browsersHelper")

const paths = require("../config/paths")
const configFactory = require("../config/webpack.config")
const createDevServerConfig = require("../config/webpack-dev-server.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) || 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("http://bit.ly/CRA-advanced-config")}`,
  )
  console.log()
}

const KILL_SIGNALS = ["SIGINT", "SIGTERM"]

// We require that you explictly set browsers and do not fall back to
// browserslist defaults.
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"
    // eslint-disable-next-line global-require, import/no-dynamic-require
    const appName = require(paths.appPackageJson).name
    const urls = prepareUrls(protocol, HOST, port)
    // Create a webpack compiler that is configured with custom messages.
    const compiler = createCompiler(webpack, config, appName, urls, useYarn)
    // Load proxy config
    // eslint-disable-next-line global-require, import/no-dynamic-require
    const proxySetting = require(paths.appPackageJson).proxy
    const proxyConfig = prepareProxy(proxySetting, paths.appPublic)
    // 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) {
        console.log(err)
        return
      }
      if (isInteractive && !process.env.NO_CLEAR) {
        clearConsole()
      }
      console.log(chalk.cyan("Starting the development server...\n"))
      openBrowser(urls.localUrlForBrowser)
    })

    KILL_SIGNALS.forEach((sig) => {
      process.on(sig, () => {
        devServer.close()
        process.exit()
      })
    })
  })
  .catch((error) => {
    if (error && error.message) {
      console.log(error.message)
    }
    process.exit(1)
  })