Transforming the window property in distinct entry points for TypeScript

Question

Transforming the window property in distinct entry points for TypeScript

During the initial page load, I am looking to transfer data from a template to a TypeScript file by attaching it to the window object. I want each page to utilize the same variable name for its specific data (window.data). An example of this can be seen in the use of window.props.

In my TypeScript entry point files for different pages (e.g. foo.ts and

bar.ts</code), I declare the data on the <code>window

object as follows:

declare global {
    interface Window {
        data: {
            foo: string;
        };
    }
}

For another page like bar.ts, the declaration would look like:

declare global {
    interface Window {
        data: {
            bar: int;
        };
    }
}

These TypeScript files are declared as separate entry points in webpack. When compiling, an error message is displayed:

TS2717: Subsequent property declarations must have the same type. Property 'data' must be of type '{ bar: string; }', but here has type '{ foo: string; }'.

Is there a way to resolve these errors without using unique names for each object?

typescript webpack

Answer 1

Answer №1

Is there a way to prevent errors without using unique names for each of these objects?

You must not declare data as two different types. The solution is to declare them to be of the same interface and utilize interface declaration merging:

// File A

declare global {
    interface IData { 
      foo: string;
    }
    interface Window {
        data: IData;
    }
}

// File B:

declare global {
    interface IData { 
      bar: number;
    }
    interface Window {
        data: IData;
    }
}

Answer 2

Is there a way to prevent errors without using unique names for each of these objects?

You must not declare data as two different types. The solution is to declare them to be of the same interface and utilize interface declaration merging:

// File A

declare global {
    interface IData { 
      foo: string;
    }
    interface Window {
        data: IData;
    }
}

// File B:

declare global {
    interface IData { 
      bar: number;
    }
    interface Window {
        data: IData;
    }
}

Answer 3

Answer №2

In a TypeScript project, it's not advisable to have contradicting sources of truth as it can complicate modeling different execution environments. The good news is that there are ways to navigate around this issue.

To tackle this challenge, consider the question: when does the data differ? Understanding this can help you shape your environment to suit your needs.

Situation one: multiple projects with a single tsconfig.json file

If you find yourself in a scenario where you have multiple projects but only one tsconfig.json configuration file, and these projects run under varying conditions, dividing your project into smaller parts with their own tsconfig.json files may be beneficial. An example of such a composite project can be found here.

For instance, a composite project could comprise server code, client code, and tests. Each of these segments may require a unique global object setup, which can be achieved by enhancing Window on a per-project basis.

Situation two: one environment with data being one of two types

If your project involves an environment where the data can exist in one of two types, it's recommended to model Window accordingly:

declare global {
  interface Window {
    data: { foo: string } | { bar: number };
  }
}

However, directly accessing properties like window.data.foo or window.data.bar is not feasible due to safety concerns. To address this limitation, leveraging assertion signatures within modules dependent on specific environments can be helpful.

function assert(condition: boolean): asserts condition {
  if (!condition) {
    throw new Error('Assertion failed');
  }
}

assert('foo' in window.data);

// Accessing foo is now possible
window.data.foo;

// However, accessing bar will result in an error
window.data.bar;

Keep in mind that this approach applies at a module level, requiring assertions in each file relying on a particular value of window.data.

Answer 4

In a TypeScript project, it's not advisable to have contradicting sources of truth as it can complicate modeling different execution environments. The good news is that there are ways to navigate around this issue.

To tackle this challenge, consider the question: when does the data differ? Understanding this can help you shape your environment to suit your needs.

Situation one: multiple projects with a single tsconfig.json file

If you find yourself in a scenario where you have multiple projects but only one tsconfig.json configuration file, and these projects run under varying conditions, dividing your project into smaller parts with their own tsconfig.json files may be beneficial. An example of such a composite project can be found here.

For instance, a composite project could comprise server code, client code, and tests. Each of these segments may require a unique global object setup, which can be achieved by enhancing Window on a per-project basis.

Situation two: one environment with data being one of two types

If your project involves an environment where the data can exist in one of two types, it's recommended to model Window accordingly:

declare global {
  interface Window {
    data: { foo: string } | { bar: number };
  }
}

However, directly accessing properties like window.data.foo or window.data.bar is not feasible due to safety concerns. To address this limitation, leveraging assertion signatures within modules dependent on specific environments can be helpful.

function assert(condition: boolean): asserts condition {
  if (!condition) {
    throw new Error('Assertion failed');
  }
}

assert('foo' in window.data);

// Accessing foo is now possible
window.data.foo;

// However, accessing bar will result in an error
window.data.bar;

Keep in mind that this approach applies at a module level, requiring assertions in each file relying on a particular value of window.data.

Transforming the window property in distinct entry points for TypeScript

Answer №1

Answer №2

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