Type Error TS2322: Cannot assign type 'Object[]' to type '[Object]'

I'm facing an issue with a code snippet that looks like this:

export class TagCloud {

    tags: [Tag];
    locations: [Location];

    constructor() {
        this.tags = new Array<Tag>();
        this.locations = new Array<Location>();
    }
}

Despite the functionality being correct, I am encountering the following errors:

error TS2322: Type 'Tag[]' is not assignable to type '[Tag]'. Property '0' is missing in type 'Tag[]'.

error TS2322: Type 'Location[]' is not assignable to type '[Lo cation]'. Property '0' is missing in type 'Location[]'.

I want to understand what mistake I might have made here (as I mentioned, the code still works as expected).

The typings are based on the es6-shim Type descriptions (https://github.com/DefinitelyTyped/DefinitelyTyped/tree/master/es6-shim).

typescriptecmascript-6typescript-typingsdefinitelytyped

Answer №1

Defining an array in TypeScript can be done in two ways:

let a: Array<number>;

or

let a: number[];

Using the syntax:

let a: [number];

actually creates a tuple, specifically a tuple of length one containing a number.
Here is an example of a tuple with multiple elements:

let a: [number, string, string];

The error occurs when assigning an array of length 0 to variables tags and locations, as the expected length should be 1.

Answer №2

If you're looking to let TypeScript know that you're creating an array of Tag, then you'll want to use Tag[].

export class TagCloud {

    tags: Tag[];
    locations: Location[];

    constructor() {
        // TypeScript is already aware of the type
        this.tags = []
        this.locations =[]
    }
}

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