Create a global variable in TypeScript

Question

In JavaScript I can just do this    something    testing     And then in another file    if  something      testing     and it will have something be defined  as long as they were called in the correct order    I can t seem to figure out how to do that in TypeScript   This is what I have tried     In a  d ts file   interface Window   something  string      Then in my main ts file    window something    testing     then in another file    if  window something       testing     And this works   But I want to be able to lose the window  part of it and just have my something be global  Is there a way to do that in TypeScript    In case someone is interested  I am really trying to setup my logging for my application   I want to be able to call log Debug from any file without having to import and create objects

User · Answer

Inside a  d ts definition file  type MyGlobalFunctionType    name  string    gt  void   If you work in the browser   you add members to the browser s window context   interface Window     myGlobalFunction  MyGlobalFunctionType     Same idea for NodeJS   declare module NodeJS     interface Global       myGlobalFunction  MyGlobalFunctionType         Now you declare the root variable  that will actually live on window or global   declare const myGlobalFunction  MyGlobalFunctionType    Then in a regular  ts file  but imported as side-effect  you actually implement it   global   or window    myGlobalFunction   function  name  string      console log  Hey     name        And finally use it elsewhere in the codebase  with either   global   or window    myGlobalFunction  Kevin     myGlobalFunction  Kevin

User · Answer

This is working for me  as described in this thread   declare let something  string  something    foo

User · Answer

im using only this  import  globalVar  from    globals   declare let window any  window globalVar   globalVar

User · Answer

globalThis is the future   First  TypeScript files have two kinds of scopes  global scope  If your file hasn t any import or export line  this file would be executed in global scope that all declaration in it are visible outside this file   So we would create global variables like this      xx d ts declare var age  number     or     xx ts    with or without declare keyword var age  number     other ts globalThis age   18    no error      All magic come from var  Replace var with let or const won t work    module scope  If your file has any import or export line  this file would be executed within its own scope that we need to extend global by declaration-merging      xx  d  ts declare global     var age  number        other ts globalThis age   18    no error      You can see more about module in official docs

User · Answer

Okay  so this is probably even uglier that what you did  but anyway      but I do the same so     What you can do to do it in pure TypeScript  is to use the eval function like so    declare var something  string  eval  something    testing       And later you ll be able to do   if  something      testing     This is nothing more than a hack to force executing the instruction without TypeScript refusing to compile  and we declare var for TypeScript to compile the rest of the code

User · Answer

I needed to make lodash global to use an existing  js file that I could not change  only require   I found that this worked   import   as lodash from  lodash     global as any      lodash

User · Answer

I m using this  interface Window       globalthing  any     declare var globalthing  any

User · Answer

I found a way that works if I use JavaScript combined with TypeScript   logging d ts   declare var log  log4javascript Logger    log-declaration js   log   null    initalize-app ts  import    log-declaration js       Call stuff to actually setup log       Similar to this  log   functionToSetupLog      This puts it in the global scope and TypeScript knows about it   So I can use it in all my files     NOTE  I think this only works because I have the allowJs TypeScript option set to true   If someone posts an pure TypeScript solution  I will accept that

User · Answer

As an addon to Dima V s answer this is what I did to make this work for me                 First declare the window global outside the class  declare let window  any      Inside the required class method  let globVarName   window globVarName

User · Answer

I spent couple hours to figure out proper way to do it  In my case I m trying to define global  log  variable so the steps were   1  configure your tsconfig json to include your defined types  src types folder  node modules - is up to you       other stuff     paths              node modules      src types         2  create file src types global d ts with following content  no imports  - this is important   feel free to change any to match your needs   use window interface instead of NodeJS if you are working with browser          IMPORTANT - do not use imports in this file     It will break global definition      declare namespace NodeJS       export interface Global           log  any           declare var log  any    3  now you can finally use implement log where its needed      in one file global log   someCoolLogger       in another file log info  hello world       or if its a variable global log    INFO

User · Answer

This is how I have fixed it   Steps    Declared a global namespace  for e g  custom d ts as below     declare global       namespace NodeJS           interface Global               Config                       export default global     Map the above created a file into  tsconfig json  as below     typeRoots     src types custom d ts       Get the above created global variable in any of the files as below    console log global config    Note     typescript version   3 0 1   In my case  the requirement was to set the global variable before boots up the application and the variable should access throughout the dependent objects so that we can get the required config properties    Hope this helps   Thank you

[typescript] Create a global variable in TypeScript

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