How to declare a global variable in JavaScript

Question

How can I declare a global variable in JavaScript

User · Answer

Declare the variable outside of functions function dosomething      var i   0     Can only be used inside function    var i       function dosomething      i   0     Can be used inside and outside the function

User · Answer

If you have to generate global variables in production code  which should be avoided  always declare them explicitly   window globalVar    This is global      While it is possible to define a global variable by just omitting var  assuming there is no local variable of the same name   doing so generates an implicit global  which is a bad thing to do and would generate an error in strict mode

User · Answer

If this is the only application where you re going to use this variable  Felix s approach is excellent  However  if you re writing a jQuery plugin  consider  quot namespacing quot   details on the quotes later     variables and functions needed under the jQuery object  For example  I m currently working on a jQuery popup menu that I ve called miniMenu  Thus  I ve defined a  quot namespace quot  miniMenu under jQuery  and I place everything there  The reason I use quotes when I talk about JavaScript namespaces is that they aren t really namespaces in the normal sense  Instead  I just use a JavaScript object and place all my functions and variables as properties of this object  Also  for convenience  I usually sub-space the plugin namespace with an i namespace for stuff that should only be used internally within the plugin  so as to hide it from users of the plugin  This is how it works     An object to define utility functions and global variables on    miniMenu   new Object       An object to define internal stuff for the plugin    miniMenu i   new Object     Now I can just do   miniMenu i globalVar   3 or   miniMenu i parseSomeStuff   function            whenever I need to save something globally  and I still keep it out of the global namespace

User · Answer

The best way is to use closures  because the window object gets very  very cluttered with properties  HTML  lt  DOCTYPE html gt   lt html gt     lt head gt       lt script type  quot text javascript quot  src  quot init js quot  gt  lt  script gt       lt script type  quot text javascript quot  gt        MYLIBRARY init   quot firstValue quot   2   quot thirdValue quot          lt  script gt       lt script src  quot script js quot  gt  lt  script gt     lt  head gt      lt body gt       lt h1 gt Hello   lt  h1 gt     lt  body gt   lt  html gt   init js  based on this answer  var MYLIBRARY   MYLIBRARY     function        var  args          Private      return           init   function Args                 args   Args                 Some other initialising                    helloWorld   function i                return  args i                           script js    Here you can use the values defined in the HTML content as if it were a global variable var a    quot Hello World  quot    MYLIBRARY helloWorld 2    alert a    Here s the plnkr  Hope it help

User · Answer

Here is a basic example of a global variable that the rest of your functions can access  Here is a live example for you  http   jsfiddle net fxCE9  var myVariable    Hello   alert  value      myVariable   myFunction1    alert  value      myVariable   myFunction2    alert  value      myVariable     function myFunction1         myVariable    Hello 1      function myFunction2         myVariable    Hello 2      If you are doing this within a jQuery ready   function then make sure your variable is inside the ready   function along with your other functions

User · Answer

Note  The question is about JavaScript  and this answer is about jQuery  which is wrong  This is an old answer  from times when jQuery was widespread  Instead  I recommend understanding scopes and closures in JavaScript  Old  bad answer With jQuery you can just do this  no matter where the declaration is   my global var    my value    And will be available everywhere  I use it for making quick image galleries  when images are spread in different places  like so   gallery      img     current   0    gallery each function i v          preload images      new Image    src   v         div   eq 0  append   lt a style  quot display inline-block quot  class  quot prev quot  gt prev lt  a gt   lt div id  quot gallery quot  gt  lt  div gt   lt a style  quot display inline-block quot  class  quot next quot  gt next lt  a gt         next   click function         current      current     gallery length - 1     0    current   1          gallery   hide   html  gallery  current   fadeIn            prev   click function         current      current    0      gallery length - 1    current - 1          gallery   hide   html  gallery  current   fadeIn         Tip  run this whole code in the console in this page  -

[javascript] How to declare a global variable in JavaScript

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