检查nodejs的全局和局部变量

Question

我不懂Javascript。 我想做的是了解python中dir（）函数的等效功能。 我想看看我当前的范围内有什么可用。

我正在使用nodejs REPL控制台：

> myglobalvariable="toto"
'toto'

现在，我想查看当前范围内的内容，因此我在控制台中输入了以下内容：

> this
{ global: [Circular],
  process: 
   process {
     title: 'nodejs',
     version: 'v4.8.2',
     moduleLoadList: 
      [ 'Binding contextify',
        'Binding natives',
        'NativeModule events',
        'NativeModule buffer',
        'Binding buffer',
        'NativeModule internal/util',
        'Binding util',
        'NativeModule timers',
        'Binding timer_wrap',
        'NativeModule _linklist',
        'NativeModule assert',
        'NativeModule util',
        'Binding uv',
        'NativeModule tty',
        'NativeModule net',
        'NativeModule stream',
        'NativeModule _stream_readable',
        'NativeModule _stream_writable',
        'NativeModule _stream_duplex',
        'NativeModule _stream_transform',
        'NativeModule _stream_passthrough',
        'NativeModule internal/net',
        'Binding cares_wrap',
        'Binding tty_wrap',
        'Binding tcp_wrap',
        'Binding pipe_wrap',
        'Binding stream_wrap',
        'NativeModule internal/repl',
        'NativeModule readline',
        'NativeModule repl',
        'NativeModule internal/module',
        'NativeModule vm',
        'NativeModule path',
        'NativeModule fs',
        'Binding fs',
        'NativeModule constants',
        'Binding constants',
        'Binding fs_event_wrap',
        'NativeModule console',
        'Binding signal_wrap',
        'NativeModule module',
        'NativeModule domain',
        'NativeModule os',
        'Binding os',
        'NativeModule string_decoder' ],
     versions: 
      { http_parser: '2.7.0',
        node: '4.8.2',
        v8: '4.5.103.46',
        uv: '1.9.1',
        zlib: '1.2.8',
        ares: '1.10.1-DEV',
        icu: '57.1',
        modules: '46',
        openssl: '1.0.2k' },
     arch: 'x64',
     platform: 'linux',
     release: 
      { name: 'node',
        lts: 'Argon',
        sourceUrl: 'https://nodejs.org/download/release/v4.8.2/node-v4.8.2.tar.gz',
        headersUrl: 'https://nodejs.org/download/release/v4.8.2/node-v4.8.2-headers.tar.gz' },
     argv: [ '/usr/bin/nodejs' ],
     execArgv: [],
     env: 
      { LS_COLORS: 'rs=0:di=01;34:ln=01;36:mh=00:pi=40;33:so=01;35:do=01;35:bd=40;33;01:cd=40;33;01:or=40;31;01:mi=00:su=37;41:sg=30;43:ca=30;41:tw=30;42:ow=34;42:st=37;44:ex=01;32:*.tar=01;31:*.tgz=01;31:*.arc=01;31:*.arj=01;31:*.taz=01;31:*.lha=01;31:*.lz4=01;31:*.lzh=01;31:*.lzma=01;31:*.tlz=01;31:*.txz=01;31:*.tzo=01;31:*.t7z=01;31:*.zip=01;31:*.z=01;31:*.Z=01;31:*.dz=01;31:*.gz=01;31:*.lrz=01;31:*.lz=01;31:*.lzo=01;31:*.xz=01;31:*.zst=01;31:*.tzst=01;31:*.bz2=01;31:*.bz=01;31:*.tbz=01;31:*.tbz2=01;31:*.tz=01;31:*.deb=01;31:*.rpm=01;31:*.jar=01;31:*.war=01;31:*.ear=01;31:*.sar=01;31:*.rar=01;31:*.alz=01;31:*.ace=01;31:*.zoo=01;31:*.cpio=01;31:*.7z=01;31:*.rz=01;31:*.cab=01;31:*.jpg=01;35:*.jpeg=01;35:*.mjpg=01;35:*.mjpeg=01;35:*.gif=01;35:*.bmp=01;35:*.pbm=01;35:*.pgm=01;35:*.ppm=01;35:*.tga=01;35:*.xbm=01;35:*.xpm=01;35:*.tif=01;35:*.tiff=01;35:*.png=01;35:*.svg=01;35:*.svgz=01;35:*.mng=01;35:*.pcx=01;35:*.mov=01;35:*.mpg=01;35:*.mpeg=01;35:*.m2v=01;35:*.mkv=01;35:*.webm=01;35:*.ogm=01;35:*.mp4=01;35:*.m4v=01;35:*.mp4v=01;35:*.vob=01;35:*.qt=01;35:*.nuv=01;35:*.wmv=01;35:*.asf=01;35:*.rm=01;35:*.rmvb=01;35:*.flc=01;35:*.avi=01;35:*.fli=01;35:*.flv=01;35:*.gl=01;35:*.dl=01;35:*.xcf=01;35:*.xwd=01;35:*.yuv=01;35:*.cgm=01;35:*.emf=01;35:*.ogv=01;35:*.ogx=01;35:*.aac=00;36:*.au=00;36:*.flac=00;36:*.m4a=00;36:*.mid=00;36:*.midi=00;36:*.mka=00;36:*.mp3=00;36:*.mpc=00;36:*.ogg=00;36:*.ra=00;36:*.wav=00;36:*.oga=00;36:*.opus=00;36:*.spx=00;36:*.xspf=00;36:',
        SSH_CONNECTION: '192.168.56.1 52776 192.168.56.102 22',
        LANG: 'fr_FR.UTF-8',
        _VIRTUALENVWRAPPER_API: ' mkvirtualenv rmvirtualenv lsvirtualenv showvirtualenv workon add2virtualenv cdsitepackages cdvirtualenv lssitepackages toggleglobalsitepackages cpvirtualenv setvirtualenvproject mkproject cdproject mktmpenv mkvirtualenv rmvirtualenv lsvirtualenv showvirtualenv workon add2virtualenv cdsitepackages cdvirtualenv lssitepackages toggleglobalsitepackages cpvirtualenv setvirtualenvproject mkproject cdproject mktmpenv',
        XDG_SESSION_ID: '2',
        USER: 'me',
        PWD: '/home/me',
        HOME: '/home/me',
        SSH_CLIENT: '192.168.56.1 52776 22',
        SSH_TTY: '/dev/pts/0',
        MAIL: '/var/mail/me',
        VIRTUALENVWRAPPER_SCRIPT: '/usr/share/virtualenvwrapper/virtualenvwrapper.sh',
        TERM: 'xterm-256color',
        SHELL: '/bin/bash',
        SHLVL: '1',
        LOGNAME: 'me',
        DBUS_SESSION_BUS_ADDRESS: 'unix:path=/run/user/1000/bus',
        XDG_RUNTIME_DIR: '/run/user/1000',
        PATH: '/usr/local/bin:/usr/bin:/bin:/usr/local/games:/usr/games',
        _: '/usr/bin/nodejs' },
     pid: 1042,
     features: 
      { debug: false,
        uv: true,
        ipv6: true,
        tls_npn: true,
        tls_alpn: true,
        tls_sni: true,
        tls_ocsp: true,
        tls: true },
     _needImmediateCallback: false,
     execPath: '/usr/bin/nodejs',
     debugPort: 5858,
     _startProfilerIdleNotifier: [Function: _startProfilerIdleNotifier],
     _stopProfilerIdleNotifier: [Function: _stopProfilerIdleNotifier],
     _getActiveRequests: [Function: _getActiveRequests],
     _getActiveHandles: [Function: _getActiveHandles],
     reallyExit: [Function: reallyExit],
     abort: [Function: abort],
     chdir: [Function: chdir],
     cwd: [Function: cwd],
     umask: [Function: umask],
     getuid: [Function: getuid],
     geteuid: [Function: geteuid],
     setuid: [Function: setuid],
     seteuid: [Function: seteuid],
     setgid: [Function: setgid],
     setegid: [Function: setegid],
     getgid: [Function: getgid],
     getegid: [Function: getegid],
     getgroups: [Function: getgroups],
     setgroups: [Function: setgroups],
     initgroups: [Function: initgroups],
     _kill: [Function: _kill],
     _debugProcess: [Function: _debugProcess],
     _debugPause: [Function: _debugPause],
     _debugEnd: [Function: _debugEnd],
     hrtime: [Function: hrtime],
     cpuUsage: [Function: cpuUsage],
     dlopen: [Function: dlopen],
     uptime: [Function: uptime],
     memoryUsage: [Function: memoryUsage],
     binding: [Function: binding],
     _linkedBinding: [Function: _linkedBinding],
     _events: 
      { newListener: [Function],
        removeListener: [Function],
        SIGWINCH: [Object] },
     _rawDebug: [Function],
     _eventsCount: 3,
     domain: [Getter/Setter],
     _maxListeners: undefined,
     EventEmitter: 
      { [Function: EventEmitter]
        EventEmitter: [Circular],
        usingDomains: true,
        defaultMaxListeners: 10,
        init: [Function],
        listenerCount: [Function] },
     _fatalException: [Function],
     _exiting: false,
     assert: [Function],
     config: { target_defaults: [Object], variables: [Object] },
     nextTick: [Function: nextTick],
     _tickCallback: [Function: _tickDomainCallback],
     _tickDomainCallback: [Function: _tickDomainCallback],
     stdout: [Getter],
     stderr: [Getter],
     stdin: [Getter],
     openStdin: [Function],
     exit: [Function],
     kill: [Function] },
  GLOBAL: [Circular],
  root: [Circular],
  Buffer: 
   { [Function: Buffer]
     poolSize: 8192,
     from: [Function],
     alloc: [Function],
     allocUnsafe: [Function],
     allocUnsafeSlow: [Function],
     isBuffer: [Function: isBuffer],
     compare: [Function: compare],
     isEncoding: [Function],
     concat: [Function],
     byteLength: [Function: byteLength] },
  clearImmediate: [Function],
  clearInterval: [Function],
  clearTimeout: [Function],
  setImmediate: [Function],
  setInterval: [Function],
  setTimeout: [Function],
  console: [Getter],
  module: 
   Module {
     id: '<repl>',
     exports: {},
     parent: undefined,
     filename: null,
     loaded: false,
     children: [],
     paths: 
      [ '/home/me/repl/node_modules',
        '/home/me/node_modules',
        '/home/node_modules',
        '/node_modules',
        '/home/me/.node_modules',
        '/home/me/.node_libraries',
        '/usr/lib/nodejs' ] },
  require: 
   { [Function: require]
     resolve: [Function],
     main: undefined,
     extensions: { '.js': [Function], '.json': [Function], '.node': [Function] },
     cache: {} },
  _: [Circular],
  myglobalvariable: 'toto' }

正如您在最后一行看到的那样，我可以看到我的全局变量。 一切对我都很好。 显示此内容相当于此时的python dir函数。

现在，让我们创建一个包含局部变量的函数：

> function addition(a,b) { local_variable=a+b; return local_variable; }

如果我调用加法函数，则在控制台中键入“ this”，这是我看到的内容：

  > this
  ...
  myglobalvariable: 'toto',
  addition: [Function: addition],
  local_variable: 9 }

我不明白为什么local_variable在那。 对我来说应该是局部变量...

我尝试了JavaScript监狱安全挑战。 我可以在此挑战中看到返回{}

但是，如果我从函数中调用它，则可以看到真正的内容。 他们如何使这成为可能？

谢谢

Answer 1

您需要使用var声明变量（或let / const）。 用var声明它会将该变量的范围限制在该函数的function addition(a,b) { var local_variable=a+b; return local_variable; } function addition(a,b) { var local_variable=a+b; return local_variable; }

如果不使用var声明它，那么即使它在函数中，也总是会在全局上下文中自动声明它。

MDN变量

如果您进一步使用let和const ，则该变量将具有块级作用域。