How do you explicitly set a new property on `window` in TypeScript?

I just found the answer to this in another Stack Overflow question's answer.

declare global {
    interface Window { MyNamespace: any; }
}

window.MyNamespace = window.MyNamespace || {};

Basically, you need to extend the existing window interface to tell it about your new property.

To keep it dynamic, just use:

(<any>window).MyNamespace

Note that this may not work with TSX because the compiler might think that the <any> is a TSX element. Check out this answer for type assertion that is compatible with TSX.

Using Svelte or TSX? None of the other answers were working for me.

Here's what I did:

(window as any).MyNamespace

As of TypeScript ^3.4.3, this solution no longer works

Or...

you can just type:

window['MyNamespace']

And you won’t get a compile error and it works the same as typing window.MyNamespace.

Globals are "evil" :) I think the best way to also have the portability is:

First you export the interface: (for example, ./custom.window.ts)

export interface CustomWindow extends Window {
    customAttribute: any;
}

Second, you import

import {CustomWindow} from './custom.window.ts';

Third, cast the global variable window with CustomWindow:

declare let window: CustomWindow;

In this way you also don't have a red line in a different IDE if you use it with existent attributes of the window object, so at the end try:

window.customAttribute = 'works';
window.location.href = '/works';

Tested with TypeScript 2.4.x and newest!

For those using the Angular CLI, it's straightforward:

File src/polyfills.ts

declare global {
  interface Window {
    myCustomFn: () => void;
  }
}

File my-custom-utils.ts

window.myCustomFn = function () {
  ...
};

If you're using IntelliJ IDEA, you also needed to change the following setting in the IDE before your new polyfills pick up:

> File
> Settings
> Languages & Frameworks
> TypeScript
> check 'Use TypeScript Service'.

The accepted answer is what I used to use, but with TypeScript 0.9.* it no longer works. The new definition of the Window interface seems to completely replace the built-in definition, instead of augmenting it.

I have taken to doing this instead:

interface MyWindow extends Window {
    myFunction(): void;
}

declare var window: MyWindow;

UPDATE: With TypeScript 0.9.5 the accepted answer is working again.

If you need to extend the window object with a custom type that requires the use of import, you can use the following method:

window.d.ts

import MyInterface from './MyInterface';

declare global {
    interface Window {
        propName: MyInterface
    }
}

See Global Augmentation in the 'Declaration Merging' section of the Handbook.

Create a file called global.d.ts, e.g., /src/@types/global.d.ts, and then define an interface like:

interface Window {
  myLib: any
}

Reference: Global .d.ts

Most of the other answers are not perfect.

Some of them just suppress the type inference for show.

Some of the others only care about global variables as namespaces, but not as interfaces/classes

I also encountered a similar problem this morning. I tried so many "solutions" on Stack Overflow, but none of them produced absolutely no type errors and enabled triggering type jumping in the IDE (WebStorm or Visual Studio Code).

Finally, from Allow module definitions to be declared as global variables #3180

I found a reasonable solution to attach typings for a global variable that acts as interface/class and namespace both.

The example is below:

// typings.d.ts
declare interface Window {
    myNamespace?: MyNamespace & typeof MyNamespace
}

declare interface MyNamespace {
    somemethod?()
}

declare namespace MyNamespace {
    // ...
}

The code above merges the typings of namespace MyNamespace and interface MyNamespace into the global variable myNamespace (the property of window).

I don't need to do this very often. The only case I have had was when using Redux DevTools with middleware.

I simply did:

const composeEnhancers = (window as any).__REDUX_DEVTOOLS_EXTENSION_COMPOSE__ || compose;

Or you could do:

let myWindow = window as any;

And then myWindow.myProp = 'my value';

After finding answers around, I think this page might be helpful:

Global augmentation

I am not sure about the history of declaration merging, but it explains why the following could work.

declare global {
    interface Window { MyNamespace: any; }
}

window.MyNamespace = window.MyNamespace || {};

From the version 3.4, TypeScript has supported globalThis. See Type-checking for globalThis.

From the above link:

// in a global file:
var abc = 100;
// Refers to 'abc' from above.
globalThis.abc = 200;
window.abc = 300; // window object can also be used.

Playground

A "global" file is a file which does not have any import/export statements. So the declaration var abc; can be written in .d.ts.

Using create-react-app v3.3 I found the easiest way to achieve this was to extend the Window type in the auto-generated react-app-env.d.ts:

interface Window {
    MyNamespace: any;
}

TypeScript does not perform typechecking on string properties.

window["newProperty"] = customObj;

Ideally, the global variable scenario should be avoided. I use it sometimes to debug an object in the browser console.

If you are using TypeScript 3.x, you may be able to omit the declare global part in the other answers and instead just use:

interface Window {
  someValue: string
  another: boolean
}

This worked with me when using TypeScript 3.3, Webpack and TSLint.

Here's how to do it, if you're using TypeScript Definition Manager!

npm install typings --global

Create typings/custom/window.d.ts:

interface Window {
  MyNamespace: any;
}

declare var window: Window;

Install your custom typing:

typings install file:typings/custom/window.d.ts --save --global

Done! Use it! TypeScript won't complain any more:

window.MyNamespace = window.MyNamespace || {};

Using

window["MyNamespace"] = window["MyNamespace"] || {};

should be all right as it is using a string property, but if you really want to have a separated window and organised your code, you can extend the window object:

interface MyNamespacedWindow extends Window {
    MyNamespace: object;
}

declare var window: MyNamespacedWindow;

First you need to declare the window object in the current scope. Because TypeScript would like to know the type of the object. Since the window object is defined somewhere else, you can not redefine it.

But you can declare it as follows:

declare var window: any;

This will not redefine the window object nor will it create another variable with name window. This means window is defined somewhere else and you are just referencing it in the current scope.

Then you can refer to your MyNamespace object simply by:

window.MyNamespace

Or you can set the new property on the window object simply by:

window.MyNamespace = MyObject

And now the TypeScript won’t complain.

For reference (this is the correct answer):

Inside a .d.ts definition file

type MyGlobalFunctionType = (name: string) => void

If you work in the browser, you add members to the browser's window context by reopening Window's interface:

interface Window {
  myGlobalFunction: MyGlobalFunctionType
}

The same idea for Node.js:

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");

Make a custom interface that extends the Window and add your custom property as optional.

Then, let the customWindow use the custom interface, but valued with the original window.

It's worked with the TypeScript 3.1.3.

interface ICustomWindow extends Window {
  MyNamespace?: any
}

const customWindow:ICustomWindow = window;

customWindow.MyNamespace = customWindow.MyNamespace {}

// In typings.d.ts(is Global)
export declare global {
    interface Window {
        __PUBLIC__: string;
    }
}

https://i.stack.imgur.com/9DPDK.png

For those who want to set a computed or dynamic property on the window object, you'll find that not possible with the declare global method. To clarify for this use case

window[DynamicObject.key] // Element implicitly has an 'any' type because type Window has no index signature

You might attempt to do something like this

declare global {
  interface Window {
    [DyanmicObject.key]: string; // error RIP
  }
}

The above will error though. This is because in TypeScript, interfaces do not play well with computed properties and will throw an error like

A computed property name in an interface must directly refer to a built-in symbol

To get around this, you can go with the suggest of casting window to <any> so you can do

(window as any)[DynamicObject.key]

Full & Short answer

1- Add typeRoots property to tsconfig.json:

{
  "compilerOptions": {
    ...
    "typeRoots": ["src/@types", "node_modules/@types"]
    ...
  }
}

2- Extend Window type

// file: src/@types/global.d.ts

declare global {
    interface Window { customProperty: <type>; }
}

(window as { test: string } & Window & typeof globalThis).test = `Hello World`;

I wanted to use this in an Angular (6) library today and it took me a while to get this to work as expected.

In order for my library to use declarations, I had to use the d.ts extension for the file that declares the new properties of the global object.

So in the end, the file ended up with something like:

/path-to-angular-workspace/angular-workspace/projects/angular-library/src/globals.d.ts

Once created, don't forget to expose it in your public_api.ts.

That did it for me.

TypeScript prevents accessing an object without assigning a type that has the desired property or already assigned to any, so you can use optional chaining:

window?.MyNamespace =  'value'

I use without declarate. My example looks like:

https://i.stack.imgur.com/qG8yc.png

[2022]:We have to extend the "window" object in our React or Nextjs project . We can use the following step to solve this issue.

Make a folder inside src folder name as types.

Make a file inside types folder name as index.d.ts

write this code inside index.d.ts file. export {}; declare global { interface Window { NameSpace: any; } } window.NameSpace= window.NameSpace|| {};

https://i.stack.imgur.com/Shpiv.png

Now one last change .

Change the "tsConfig.json" file. to inherit both the node module type and our types.

{
  "compilerOptions": {
   ...
    "typeRoots": [
      "./node_modules/@types",
      "./src/types"
    ],
 ....
}

https://i.stack.imgur.com/Pyf4N.png