process.env.NODE_ENV是什么？
什么是process.env
process.env 是 Node.js 中的一个环境对象。其中保存着系统的环境的变量信息。可使用 Node.js 命令行工具直接进行查看。
process是node的全局变量，表示的是当前的node进程，并且process有env这个属性，process.env包含着关于系统环境的信息，但是process.env中并不存在NODE_ENV这个东西。也就是没有NODE_ENV这个属性。
在项目中，NODE_ENV是一个用户自定义的变量，在webpack中它的用途是判断生产环境或开发环境。
为了查看 process的基本信息，我们可以在文件夹中 新建一个process.js文件，在里面加一句代码console.log(process);然后进入该文件夹，执行node process.js可以在命令行中打印如下信息：
$ 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' ] } }
如上就可以看到 process是node的全局变量，并且process有env这个属性，但是没有NODE_ENV这个属性。
