Fix - Type 'typeof globalThis' has no index signature in TS

Fix - Type 'typeof globalThis' has no index signature in TS #

The error "Element implicitly has an 'any' type because type 'typeof globalThis' has no index signature" occurs when we try to access a property that doesn't exist on the global object. To solve the error, extend the global object and add types for the necessary properties.

Here is an example of how the error occurs.

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// ⛔️ Error: Element implicitly has an 'any'
// type because type 'typeof globalThis'
// has no index signature.ts(7017)
global.hello = 'world';

We tried to access a property that doesn't exist on the global object and got the error.

To solve this, we have to add typings for the properties and methods we intend to access on the global object.

In your src directory, create a types directory that contains the following index.d.ts file:

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/* eslint-disable no-var */

declare global {
  var example: string;
  function sum(a: number, b: number): number;
}

export {};

We added an example property that has a type of string and a sum method.

Make sure to use the var keyword to add typings for properties you intend to set and use in other files.

You need to add the names and types of all of the properties you intend to access on the global object.

For example, if you don't know the type of the specific property and want to turn off type checking, set it to any.

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/* eslint-disable no-var */

declare global {
  var example: string;
  function sum(a: number, b: number): number;
}

export {};

Now, I'm able to set and access the specified property on the global object without getting any errors.

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global.example = 'hello world';

global.sum = function (a: number, b: number) {
  return a + b;
};

console.log(global.example); // 👉️ "hello world"

console.log(global.sum(15, 25)); // 👉️ 40

Note that you might still be getting an error in your terminal if you are using ts-node.

The problem is with ts-node not recognizing local declaration files.

To solve this, use the --files flag with your ts-node command, so instead of ts-node ./src/index.ts you should run ts-node --files ./src/index.ts.

I'm using nodemon with ts-node and here are the contents of my nodemon.json file.

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{
  "watch": ["src"],
  "ext": ".ts,.js",
  "ignore": [],
  "exec": "ts-node --files ./src/index.ts"
}

After adding the --files flag (only required if using ts-node), restart your server and you should be good to go.

Note that this makes the sum function and the example property accessible directly (globally) and on the global object.

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global.example = 'hello world';

global.sum = function (a: number, b: number) {
  return a + b;
};

console.log(global.example); // 👉️ "hello world"
console.log(global.sum(15, 25)); // 👉️ 40

console.log(example); // 👉️ "hello world"
console.log(sum(5, 15)); // 👉️ 20

If you are still getting an error in your IDE, try adding the path to your types directory to your tsconfig.json file.

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

We used the export {} line in our index.d.ts file to mark it as an external module. A module is a file that contains at least 1 import or export statement. We are required to do that to be able to augment the global scope.

You should add the names (and types) of all of the properties you intend to access on the global object.

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/* eslint-disable no-var */

declare global {
  var example: any; // 👈️ disables type checking for property
  function sum(a: number, b: number): number;
}

export {};

The provided file simply adds an example property with a type of any and a sum method, which is most likely not what you need.

TypeScript looks for .d.ts files in the same places it looks for your regular .ts files, which is determined by the include and exclude settings in your tsconfig.json file.

TypeScript will merge the typings you declared on the global object with the original typings, so you will be able to access properties and methods from both declarations.