Node js global variables

Question

I asked here  Does Node js require inheritance  And I was told that I can set variables to the global scope by leaving out the variable  This does not work for me  That is  the following does not make the   available on required files      require  underscore     I can set with Express js s app set and have it available elsewhere though  Is that how this is supposed to work

User · Accepted Answer

You can use global like so   global     require  underscore

User · Answer

In Node js  you can set global variables via the  quot global quot  or  quot GLOBAL quot  object  GLOBAL     require  underscore       But you  quot shouldn t quot  do this   see note below   or more usefully    GLOBAL window   GLOBAL      Like in the browser  From the Node js source  you can see that these are aliased to each other  node-v0 6 6 src node js  28      global   this  128     global GLOBAL   global   In the code above   quot this quot  is the global context  With the CommonJS module system  which Node js uses   the  quot this quot  object inside of a module  i e    quot your code quot   is not the global context   For proof of this  see below where I spew the  quot this quot  object and then the giant  quot GLOBAL quot  object  console log   nTHIS     console log this   console log   nGLOBAL     console log global       Outputs      THIS      GLOBAL    ArrayBuffer   Function  ArrayBuffer     Int8Array     Function  BYTES PER ELEMENT  1      Uint8Array     Function  BYTES PER ELEMENT  1      Int16Array     Function  BYTES PER ELEMENT  2      Uint16Array     Function  BYTES PER ELEMENT  2      Int32Array     Function  BYTES PER ELEMENT  4      Uint32Array     Function  BYTES PER ELEMENT  4      Float32Array     Function  BYTES PER ELEMENT  4      Float64Array     Function  BYTES PER ELEMENT  8      DataView   Function  DataView     global   Circular     process       EventEmitter   Function  EventEmitter        title   node        assert   Function        version   v0 6 5         tickCallback   Function        moduleLoadList           Binding evals            Binding natives            NativeModule events            NativeModule buffer            Binding buffer            NativeModule assert            NativeModule util            NativeModule path            NativeModule module            NativeModule fs            Binding fs            Binding constants            NativeModule stream            NativeModule console            Binding tty wrap            NativeModule tty            NativeModule net            NativeModule timers            Binding timer wrap            NativeModule  linklist          versions          node   0 6 5           v8   3 6 6 11           ares   1 7 5-DEV           uv   0 6           openssl   0 9 8n          nextTick   Function        stdout   Getter        arch   x64        stderr   Getter        platform   darwin        argv     node     workspace zd zgap darwin-js index js          stdin   Getter        env          TERM PROGRAM   iTerm app            COM GOOGLE CHROME FRAMEWORK SERVICE PROCESS USERS DDOPSON LIBRARY APPLICATION SUPPORT GOOGLE CHROME SOCKET     tmp launch-nNl1vo ServiceProcessSocket           TERM   xterm           SHELL    bin bash           TMPDIR    var folders 2h 2hQmtmXlFT4yVGtr5DBpdl9LAiQ -Tmp-            Apple PubSub Socket Render    tmp launch-9Ga0PT Render           USER   ddopson           COMMAND MODE   unix2003           SSH AUTH SOCK    tmp launch-sD905b Listeners             CF USER TEXT ENCODING   0x12D732E7 0 0           PATH    usr local bin  usr bin  bin  usr sbin  sbin   bin  usr X11 bin           PWD    workspace zd zgap darwin-js           LANG   en US UTF-8           ITERM PROFILE   Default           SHLVL   1           COLORFGBG   7 0           HOME    Users ddopson           ITERM SESSION ID   w0t0p0           LOGNAME   ddopson           DISPLAY    tmp launch-l9RQXI org x 0           OLDPWD    workspace zd zgap darwin-js external                 index js          openStdin   Function        exit   Function        pid  10321       features          debug  false          uv  true          ipv6  true          tls npn  false          tls sni  true          tls  true         kill   Function        execPath    usr local bin node        addListener   Function         needTickCallback   Function        on   Function        removeListener   Function        reallyExit   Function        chdir   Function        debug   Function        error   Function        cwd   Function        watchFile   Function        umask   Function        getuid   Function        unwatchFile   Function        mixin   Function        setuid   Function        setgid   Function        createChildProcess   Function        getgid   Function        inherits   Function         kill   Function         byteLength   Function        mainModule          id               exports              parent  null          filename    workspace zd zgap darwin-js index js           loaded  false          exited  false          children              paths   Object           debugProcess   Function        dlopen   Function        uptime   Function        memoryUsage   Function        uvCounters   Function        binding   Function       GLOBAL   Circular     root   Circular     Buffer        Function  Buffer       poolSize  8192       isBuffer   Function  isBuffer        byteLength   Function         charsWritten  8      setTimeout   Function     setInterval   Function     clearTimeout   Function     clearInterval   Function     console   Getter     window   Circular     navigator             Note  regarding setting  quot GLOBAL   quot   in general you should just do var     require  underscore     Yes  you do that in every single file that uses Underscore js  just like how in Java you do import com foo bar   This makes it easier to figure out what your code is doing because the linkages between files are  explicit   It is mildly annoying  but a good thing        That s the preaching  There is an exception to every rule   I have had precisely exactly one instance where I needed to set  quot GLOBAL   quot    I was creating a system for defining  quot configuration quot  files which were basically JSON  but were  quot written in JavaScript quot  to allow a bit more flexibility   Such configuration files had no  require  statements  but I wanted them to have access to Underscore js  the entire system was predicated on Underscore js and Underscore js templates   so before evaluating the  quot configuration quot   I would set  quot GLOBAL   quot    So yeah  for every rule  there s an exception somewhere   But you had better have a darn good reason and not just  quot I get tired of typing  require   so I want to break with the convention quot

User · Answer

I agree that using the global GLOBAL namespace for setting anything global is bad practice and don t use it at all in theory  in theory being the operative word   However  yes  the operative  I do use it for setting custom Error classes     Some global configuration file that gets called in initialisation  global MyError    Function of MyError    Yes  it is taboo here  but if your site project uses custom errors throughout the place  you would basically need to define it everywhere  or at least somewhere to   Define the Error class in the first place In the script where you re throwing it In the script where you re catching it  Defining my custom errors in the global namespace saves me the hassle of require ing my customer error library  Imaging throwing a custom error where that custom error is undefined

User · Answer

Use a global namespace like global MYAPI       global MYAPI     require  underscore     All other posters talk about the bad pattern involved  So leaving that discussion aside  the best way to have a variable defined globally  OP s question  is through namespaces  Tip  Development Using Namespaces

User · Answer

You can just use the global object   var X     a    b    c    global x   X   console log x       a    b    c

User · Answer

The other solutions that use the GLOBAL keyword are a nightmare to maintain readability   namespace pollution and bugs  when the project gets bigger  I ve seen this mistake many times and had the hassle of fixing it  Use a JavaScript file and then use module exports  Example  File globals js var Globals          domain   www MrGlobal com      module exports   Globals   Then if you want to use these  use require  var globals   require  globals        lt  lt  globals js path globals domain     lt  lt  Domain

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