Encountering a "property is missing in type { [key: string]: any; }" error while using TestCafe typed Context

Question

Encountering a "property is missing in type { [key: string]: any; }" error while using TestCafe typed Context

Despite my experience using Typescript, I still come across challenges that stump me from time to time.

In a recent Github issue, the function passed into any test hook using a typed context is causing an error:

Property 'color' is missing in type '{ [key: string]: any; }' but required in type 'MyContext'

The code snippet from the Github issue triggering the problem is as follows:

interface MyContext {
    color: string
}

interface TestControllerEx<TContext> extends Omit<TestController, 'ctx'> {
    ctx: TContext;
}

fixture`Fixture1`.beforeEach(async (t: TestControllerEx<MyContext>) => {
    t.ctx.color = 'red' // strongly typed!
});

test('Test1', async (t: TestControllerEx<MyContext>) => {
    await t.expect(t.ctx.color).eql('red'); // 'red' strongly typed!
});

To work around the issue, I have made the color property in MyContext optional. However, I am keen to understand the root cause of this problem.

The TestController interface in TestCafe types the ctx property as { [key: string]: any }. Shouldn't the generic type passed into TestControllerEx fulfill this requirement? I have attempted having TContext extend the { [key: string]: any } index signature directly without success.

Is this issue related to TestCafe's typings or am I overlooking something specific to Typescript?

I would greatly appreciate any assistance. Thank you!

typescript typescript-generics testcafe

Answer 1

Answer №1

From what I understand, there isn't a straightforward way to accomplish your objective. One workaround is to create a custom FixtureFn interface and utilize the fixture object as its implementation.

get-fixture-with-custom-ctx.ts script:

import 'testcafe';

export function getFixtureWithCustomCtx<MyContext> () {
    interface TestControllerEx extends TestController {
        ctx: MyContext;
    }

    // @ts-ignore
    interface MyFixture extends FixtureFn {
        beforeEach: (fn: (t: TestControllerEx) => Promise<any>) => MyFixture;
    }
    return fixture as MyFixture;
}

test.ts file:

import { getFixtureWithCustomCtx } from './fixture';

interface MyContext {
    color: string;
}

const fixture = getFixtureWithCustomCtx<MyContext>();

fixture`My fixture`
    .page('about:blank')
    .beforeEach(async t => {
        t.ctx.color = 'red';
        t.ctx.style = 'inline';
    });

test('Test1', async t => {
    await t.expect(t.ctx.color).eql('red');
});

By following this approach, TypeScript rules will only be broken in one specific file where you export the fixture with the desired context for use anywhere else.

Answer 2

From what I understand, there isn't a straightforward way to accomplish your objective. One workaround is to create a custom FixtureFn interface and utilize the fixture object as its implementation.

get-fixture-with-custom-ctx.ts script:

import 'testcafe';

export function getFixtureWithCustomCtx<MyContext> () {
    interface TestControllerEx extends TestController {
        ctx: MyContext;
    }

    // @ts-ignore
    interface MyFixture extends FixtureFn {
        beforeEach: (fn: (t: TestControllerEx) => Promise<any>) => MyFixture;
    }
    return fixture as MyFixture;
}

test.ts file:

import { getFixtureWithCustomCtx } from './fixture';

interface MyContext {
    color: string;
}

const fixture = getFixtureWithCustomCtx<MyContext>();

fixture`My fixture`
    .page('about:blank')
    .beforeEach(async t => {
        t.ctx.color = 'red';
        t.ctx.style = 'inline';
    });

test('Test1', async t => {
    await t.expect(t.ctx.color).eql('red');
});

By following this approach, TypeScript rules will only be broken in one specific file where you export the fixture with the desired context for use anywhere else.

Answer 3

Answer №2

In this specific scenario, the use of Typescript is essential. The example shows how TestControllerEx extends all properties from TestController at the top level without doing so for embedded properties like ctx. It then proceeds to override the properties of ctx with a more robust type. This restriction ensures that arbitrary values cannot be assigned to the ctx property. To tackle this issue, an additional definition can be added in the MyContext, as demonstrated below:

import { Selector } from 'testcafe';

interface MyContext {
    color: string;
    [key: string]: any;
}

interface TestControllerEx<TContext> extends Omit<TestController, 'ctx'> {
    ctx: TContext;
}

fixture`Fixture1`.beforeEach(async (t: TestControllerEx<MyContext>) => {
    t.ctx.color = 'red' // strongly typed!
    t.ctx.style = 'inline ' // strongly typed!
});

test('Test1', async (t: TestControllerEx<MyContext>) => {
    await t.expect(t.ctx.color).eql('red'); // 'red' strongly typed!
});

Answer 4

In this specific scenario, the use of Typescript is essential. The example shows how TestControllerEx extends all properties from TestController at the top level without doing so for embedded properties like ctx. It then proceeds to override the properties of ctx with a more robust type. This restriction ensures that arbitrary values cannot be assigned to the ctx property. To tackle this issue, an additional definition can be added in the MyContext, as demonstrated below:

import { Selector } from 'testcafe';

interface MyContext {
    color: string;
    [key: string]: any;
}

interface TestControllerEx<TContext> extends Omit<TestController, 'ctx'> {
    ctx: TContext;
}

fixture`Fixture1`.beforeEach(async (t: TestControllerEx<MyContext>) => {
    t.ctx.color = 'red' // strongly typed!
    t.ctx.style = 'inline ' // strongly typed!
});

test('Test1', async (t: TestControllerEx<MyContext>) => {
    await t.expect(t.ctx.color).eql('red'); // 'red' strongly typed!
});

Encountering a "property is missing in type { [key: string]: any; }" error while using TestCafe typed Context

Answer №1

Answer №2

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