How to declare a global variable in a js file

Question

I need a few global variables that I need in all  js files   For example  consider the following 4 files    global js js1 js js2 js js3 js   Is there a way that I can declare 3 global variables in global js and access them in any of the other 3  js files considering I load all the above 4 files into a HTML document   Can someone please tell me if this is possible or is there a work around to achieve this

User · Answer

Have you tried it   If you do   var HI    Hello World     In global js  And then do   alert HI     In js1 js it will alert it fine  You just have to include global js prior to the rest in the HTML document   The only catch is that you have to declare it in the window s scope  not inside any functions    You could just nix the var part and create them that way  but it s not good practice

User · Answer

As mentioned above  there are issues with using the top-most scope in your script file  Here is another issue  The script file might be run from a context that is not the global context in some run-time environment   It has been proposed to assign the global to window directly  But that is also run-time dependent and does not work in Node etc  It goes to show that portable global variable management needs some careful consideration and extra effort  Maybe they will fix it in future ECMS versions   For now  I would recommend something like this to support proper global management for all run-time environments          Exports the given object into the global context      var exportGlobal   function name  object        if  typeof global       undefined                 Node js         global name    object            else if  typeof window       undefined                JS with GUI  usually browser          window name    object            else           throw new Error  Unkown run-time environment  Currently only browsers and Node js are supported                   export exportGlobal itself exportGlobal  exportGlobal   exportGlobal       create a new global namespace exportGlobal  someothernamespace          It s a bit more typing  but it makes your global variable management future-proof   Disclaimer  Part of this idea came to me when looking at previous versions of stacktrace js    I reckon  one can also use Webpack or other tools to get more reliable and less hackish detection of the run-time environment

User · Answer

Yes you can access them  You should declare them in  public space   outside any functions  as   var globalvar1    value     You can access them later on  also in other files

User · Answer

Just define your variables in global js outside a function scope      global js var global1    I m a global    var global2    So am I        other js-file function testGlobal          alert global1       To make sure that this works you have to include link to global js before you try to access any variables defined in that file    lt html gt       lt head gt           lt  -- Include global js first -- gt           lt script src   YOUR PATH global js  type  text javascript  gt  lt  script gt           lt  -- Now we can reference variables  objects  functions etc                defined in global js -- gt           lt script src   YOUR PATH otherJsFile js  type  text javascript  gt  lt  script gt       lt  head gt             lt  html gt    You could  of course  link in the script tags just before the closing  lt body gt -tag if you do not want the load of js-files to interrupt the initial page load

User · Answer

The recommended approach is   window greeting    Hello World     You can then access it within any function   function foo         alert greeting      Hello World     alert window  greeting        Hello World     alert window greeting      Hello World   recommended       This approach is preferred for two reasons    The intent is explicit  The use of the var keyword can easily lead to declaring global vars that were intended to be local or vice versa  This sort of variable scoping is a point of confusion for a lot of Javascript developers  So as a general rule  I make sure all variable declarations are preceded with the keyword var or the prefix window  You standardize this syntax for reading the variables this way as well which means that a locally scoped var doesn t clobber the global var or vice versa  For example what happens here is ambiguous     nbsp    greeting    Aloha     function foo          greeting    Hello      overrides global       function bar greeting       alert greeting        foo     bar  Howdy       does it alert  Hello  or  Howdy      However  this is much cleaner and less error prone  you don t really need to remember all the variable scoping rules     function foo          window greeting    Hello        function bar greeting       alert greeting        foo     bar  Howdy       alerts  Howdy

[javascript] How to declare a global variable in a .js file

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