How do I define global variables in CoffeeScript

Question

On Coffeescript org   bawbag    x  y  - gt      z    x   y   bawbag 5  10     would compile to   var bawbag  bawbag   function x  y      var z    return  z    x   y       bawbag 5  10     compiling via coffee-script under node js wraps that so    function       var bawbag    bawbag   function x  y        var z      return  z    x   y           bawbag 5  10      call this     Docs say      If you d like to create top-level variables for other scripts to use    attach them as properties on window  or on the exports object in   CommonJS  The existential operator  covered below   gives you a   reliable way to figure out where to add them  if you re targeting both   CommonJS and the browser  root   exports   this   How do I define Global Variables then in CoffeeScript  What does  attach them as properties on window  mean

User · Answer

To me it seems  atomicules has the simplest answer  but I think it can be simplified a little more  You need to put an   before anything you want to be global  so that it compiles to this anything and this refers to the global object   so      bawbag    x  y  - gt      z    x   y   bawbag 5  10    compiles to     this bawbag   function x  y      var z    return z   x   y     bawbag 5  10     and works inside and outside of the wrapper given by node js   function         this bawbag   function x  y          var z        return z   x   y             console log bawbag 5 13      works here    call this    console log bawbag 5 11      works here

User · Answer

Since coffeescript is rarely used on it s own  you can use global variable supplied by either node js or browserify  and any descendants like coffeeify  gulp build scripts  etc    In node js global is global namespace   In browserify global is equal to window   So  just    somefunc   - gt    global variable   123

User · Answer

Since coffee script has no var statement it automatically inserts it for all variables in the coffee-script  that way it prevents the compiled JavaScript version from leaking everything into the global namespace     So since there s no way to make something  leak  into the global namespace from the coffee-script side of things on purpose  you need to define your global variables as properties of the global object      attach them as properties on window   This means you need to do something like window foo    baz    which handles the browser case  since there the global object is the window   Node js  In Node js there s no window object  instead there s the exports object that gets passed into the wrapper that wraps the Node js module  See  https   github com ry node blob master src node js L321    so in Node js what you would need to do is exports foo    baz     Now let us take a look at what it states in your quote from the docs           targeting both CommonJS and the browser  root   exports   this   This is obviously coffee-script  so let s take a look into what this actually compiles to     var root  root    typeof exports      undefined   amp  amp  exports     null    exports   this    First it will check whether exports is defined  since trying to reference a non existent variable in JavaScript would otherwise yield an SyntaxError  except when it s used with typeof   So if exports exists  which is the case in Node js  or in a badly written WebSite     root will point to exports  otherwise to this  So what s this    function          call this     Using  call on a function will bind the this inside the function to the first parameter passed  in case of the browser this would now be the window object  in case of Node js it would be the global context which is also available as the global object     But since you have the require function in Node js  there s no need to assign something to the global object in Node js  instead you assign to the exports object which then gets returned by the require function   Coffee-Script  After all that explanation  here s what you need to do     root   exports   this root foo   - gt   Hello World    This will declare our function foo in the global namespace  whatever that happens to be   That s all

User · Answer

You can pass -b option when you compile code via coffee-script under node js  The compiled code will be the same as on coffeescript org

User · Answer

If you re a bad person  I m a bad person    you can get as simple as this   - gt       As in    - gt      im a terrible programmer   yes console log im a terrible programmer     This works  because when invoking a Reference to a Function    bare     that is  func    instead of new func   or obj func     something commonly referred to as the    function-call invocation pattern     always binds this to the global object for that execution context   The CoffeeScript above simply compiles to  function    return this       so we re exercising that behavior to reliably access the global object

User · Answer

Ivo nailed it  but I ll mention that there is one dirty trick you can use  though I don t recommend it if you re going for style points  You can embed JavaScript code directly in your CoffeeScript by escaping it with backticks   However  here s why this is usually a bad idea  The CoffeeScript compiler is unaware of those variables  which means they won t obey normal CoffeeScript scoping rules  So    foo    bar   foo    something else    compiles to  foo    bar   var foo    something else     and now you ve got yourself two foos in different scopes  There s no way to modify the global foo from CoffeeScript code without referencing the global object  as Ivy described   Of course  this is only a problem if you make an assignment to foo in CoffeeScript   if foo became read-only after being given its initial value  i e  it s a global constant   then the embedded JavaScript solution approach might be kinda sorta acceptable  though still not recommended

User · Answer

I think what you are trying to achieve can simply be done like this    While you are compiling the coffeescript  use the  -b  parameter   -b   --bare Compile the JavaScript without the top-level function safety wrapper   So something like this   coffee -b --compile somefile coffee whatever js  This will output your code just like in the CoffeeScript org site

User · Answer

To add to Ivo Wetzel s answer  There seems to be a shorthand syntax for exports   this that I can only find documented mentioned on a Google group posting   I e  in a web page to make a function available globally you declare the function again with an   prefix    lt script type  text coffeescript  gt       aglobalfunction   aglobalfunction      - gt           alert  Hello    lt  script gt    lt a href  javascript aglobalfunction     gt Click me  lt  a gt

[javascript] How do I define global variables in CoffeeScript?

so...

compiles to...

and works inside and outside of the wrapper given by node.js

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