How can I declare a global variable in Angular 2 Typescript

Question

I would like some variables to be accessible everywhere in an Angular 2 in the Typescript language  How should I go about accomplishing this

User · Answer

I like the answer of  supercobra  but I would use the const keyword as it is in ES6 already available               File globals ts         use strict    export const sep      export const version  string  22 2 2

User · Answer

I think the best way is to share an object with global variables throughout your application by exporting and importing it where you want   First create a new  ts file for example globals ts and declare an object  I gave it an Object type but you also could use an any type or     export let globalVariables  Object      version   1 3 3 7    author   0x1ad2    everything  42      After that import it  import  globalVariables  from  path to your globals ts    And use it  console log globalVariables

User · Answer

See for example Angular 2 - Implementation of shared services     Injectable    export class MyGlobals     readonly myConfigValue string    abc       NgModule     providers   MyGlobals             class MyComponent     constructor private myGlobals MyGlobals        console log myGlobals myConfigValue           or provide individual values   NgModule     providers    provide   myConfigValue   useValue   abc               class MyComponent     constructor  Inject  myConfigValue   private myConfigValue string        console log myConfigValue

User · Answer

I don t know the best way  but the easiest way if you want to define a global variable inside of a component is to use window variable to write like this   window GlobalVariable    what ever    you don t need to pass it to bootstrap or import it other places  and it is globally accessibly to all JS  not only angular 2 components

User · Answer

That s the way I use it   global ts  export var server  string    http   localhost 4200    export var var2  number   2  export var var3  string    var3     to use it just import like that   import   Injectable   from   angular core   import   Http  Headers  RequestOptions   from   angular http   import   Observable   from  rxjs Rx   import   as glob from     shared global      lt    HERE   Injectable   export class AuthService       private AuhtorizationServer   glob server     EDITED  Droped     prefixed as recommended

User · Answer

Here is the simplest solution w o Service nor Observer   Put the global variables in a file an export them               File globals ts         use strict    export const sep      export const version  string  22 2 2         To use globals in another file use an import statement  import   as myGlobals from  globals    Example                File heroes component ts        import  Component  OnInit  from  angular2 core   import  Router  from  angular2 router   import  HeroService  from    hero service   import  HeroDetailComponent  from    hero-detail component   import  Hero  from    hero   import   as myGlobals from  globals      lt      this one    Updated     export class HeroesComponent implements OnInit       public heroes  Hero        public selectedHero  Hero                        Here we access the global var reference               public helloString  string  hello     myGlobals sep     there                                    Thanks  eric-martinez

User · Answer

IMHO for Angular2  v2 2 3  the best way is to add services that contain the global variable and inject them into components without the providers tag inside the  Component annotation  By this way you are able to share information between components   A sample service that owns a global variable   import   Injectable   from   angular core    Injectable   export class SomeSharedService     public globalVar           A sample component that updates the value of your global variable   import   SomeSharedService   from     services index     Component     templateUrl           export class UpdatingComponent      constructor private someSharedService  SomeSharedService         updateValue         this someSharedService globalVar    updated value           A sample component that reads the value of your global variable   import   SomeSharedService   from     services index     Component     templateUrl           export class ReadingComponent      constructor private someSharedService  SomeSharedService         readValue         let valueReadOut   this someSharedService globalVar         do something with the value read out            Note that providers    SomeSharedService   should not be added to your  Component annotation  By not adding this line injection will always give you the same instance of SomeSharedService  If you add the line a freshly created instance is injected

User · Answer

I like the solution from  supercobra too   I just would like to improve it slightly  If you export an object which contains all the constants  you could simply use es6 import the module without using require    I also used Object freeze to make the properties become true constants  If you are interested in the topic  you could read this post      global ts   export const GlobalVariable   Object freeze        BASE API URL   http   example com               more of your variables        Refer the module using import     anotherfile ts that refers to global constants import   GlobalVariable   from    path global    export class HeroService       private baseApiUrl   GlobalVariable BASE API URL             more code

User · Answer

Create Globals class in app globals ts   import   Injectable   from   angular core    Injectable   export class Globals      VAR1    value1       VAR2    value2       In your component   import   Globals   from    globals     Component       selector   my-app       providers    Globals        template    lt h1 gt My Component   globals VAR1   lt h1  gt      export class AppComponent       constructor private globals  Globals             Note  You can add Globals service provider directly to the module instead of the component  and you will not need to add as a provider to every component in that module    NgModule       imports             declarations             providers    Globals        bootstrap    AppComponent      export class AppModule

User · Answer

A shared service is the best approach export class SharedService     globalVar string     But you need to be very careful when registering it to be able to share a single instance for whole your application  You need to define it when registering your application  bootstrap AppComponent   SharedService     But not to define it again within the providers attributes of your components   Component             providers    SharedService       No             Otherwise a new instance of your service will be created for the component and its sub-components  You can have a look at this question regarding how dependency injection and hierarchical injectors work in Angular 2   What  39 s the best way to inject one service into another in angular 2  Beta    You should notice that you can also define Observable properties in the service to notify parts of your application when your global properties change  export class SharedService     globalVar string    globalVarUpdate Observable lt string gt     globalVarObserver Observer     constructor         this globalVarUpdate   Observable create  observer Observer    gt          this globalVarObserver   observer                 updateGlobalVar newValue string        this globalVar   newValue      this globalVarObserver next this globalVar          See this question for more details   Delegation  EventEmitter or Observable in Angular

[typescript] How can I declare a global variable in Angular 2 / Typescript?

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