问题描述
在分析www.js里面的代码的时候，有：
var port = normalizePort(process.env.PORT || '3001'); app.set('port', port);
产生两个疑问：
- 这里为什么不直接设
app.set(‘port’,‘3001’)? process.env.PORT是什么？
问题解疑
process.env.PORT是环境变量
在node中，有全局变量process表示的是当前的node进程。process.env包含着关于系统环境的信息。但是process.env中并不存在PORT这个变量。PORT是用户一个自定义的变量。
我们可以通过以下代码，来查看process的值：
console.log(process);
输出结果为：
$ node process.js process { title: 'node', version: 'v4.4.4', moduleLoadList: [....], versions: { http_parser: '2.5.2', node: '4.4.4', v8: '4.5.103.35', uv: '1.8.0', zlib: '1.2.8', ares: '1.10.1-DEV', icu: '56.1', modules: '46', openssl: '1.0.2h' }, arch: 'x64', platform: 'darwin', release: { name: 'node', lts: 'Argon', sourceUrl: 'https://nodejs.org/download/release/v4.4.4/node-v4.4.4.tar.gz', headersUrl: 'https://nodejs.org/download/release/v4.4.4/node-v4.4.4-headers.tar.gz' }, argv: [ '/Users/tugenhua/.nvm/versions/node/v4.4.4/bin/node', '/Users/tugenhua/个人demo/process.js' ], execArgv: [], env: { TERM_PROGRAM: 'Apple_Terminal', SHELL: '/bin/zsh', TERM: 'xterm-256color', TMPDIR: '/var/folders/l7/zndlx1qs05v29pjhvkgpmhjm0000gn/T/', Apple_PubSub_Socket_Render: '/private/tmp/com.apple.launchd.7Ax4C1EWMx/Render', TERM_PROGRAM_VERSION: '404', TERM_SESSION_ID: '82E05668-442D-4180-ADA3-8CF64D85E5A9', USER: 'tugenhua', SSH_AUTH_SOCK: '/private/tmp/com.apple.launchd.MYOMheYcL3/Listeners', PATH: '/Users/tugenhua/.nvm/versions/node/v4.4.4/bin:/usr/local/bin:/usr/bin:/bin:/usr/sbin:/sbin', PWD: '/Users/tugenhua/个人demo', LANG: 'zh_CN.UTF-8', XPC_FLAGS: '0x0', XPC_SERVICE_NAME: '0', SHLVL: '1', HOME: '/Users/tugenhua', LOGNAME: 'tugenhua', SECURITYSESSIONID: '186a8', OLDPWD: '/Users/tugenhua/工作文档/sns_pc', ZSH: '/Users/tugenhua/.oh-my-zsh', PAGER: 'less', LESS: '-R', LC_CTYPE: 'zh_CN.UTF-8', LSCOLORS: 'Gxfxcxdxbxegedabagacad', NVM_DIR: '/Users/tugenhua/.nvm', NVM_NODEJS_ORG_MIRROR: 'https://nodejs.org/dist', NVM_IOJS_ORG_MIRROR: 'https://iojs.org/dist', NVM_RC_VERSION: '', MANPATH: '/Users/tugenhua/.nvm/versions/node/v4.4.4/share/man:/usr/local/share/man:/usr/share/man:/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.13.sdk/usr/share/man:/Applications/Xcode.app/Contents/Developer/usr/share/man:/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/share/man', NVM_PATH: '/Users/tugenhua/.nvm/versions/node/v4.4.4/lib/node', NVM_BIN: '/Users/tugenhua/.nvm/versions/node/v4.4.4/bin', _: '/Users/tugenhua/.nvm/versions/node/v4.4.4/bin/node', __CF_USER_TEXT_ENCODING: '0x1F5:0x19:0x34' }, pid: 14034, features: { debug: false, uv: true, ipv6: true, tls_npn: true, tls_sni: true, tls_ocsp: true, tls: true }, _needImmediateCallback: false, config: {}, nextTick: [Function: nextTick], _tickCallback: [Function: _tickCallback], _tickDomainCallback: [Function: _tickDomainCallback], stdout: [Getter], stderr: [Getter], stdin: [Getter], openStdin: [Function], exit: [Function], kill: [Function], mainModule: Module { id: '.', exports: {}, parent: null, filename: '/Users/tugenhua/个人demo/process.js', loaded: false, children: [], paths: [ '/Users/tugenhua/个人demo/node_modules', '/Users/tugenhua/node_modules', '/Users/node_modules', '/node_modules' ] } }
我们可以看到在env这个变量里面，没有PORT变量。
所以对于代码：
var port = normalizePort(process.env.PORT || '3001'); app.set('port', port);
是先考虑到node的进程的环境变量的端口，再考虑3001端口号。
