CODEWITHSUNDEEP
typescript
Bradd
Bradd

Reputation: 196

Create an interface for an Array with properties

Is it possible to create an interface that reflects the type generated by:

const foo = Object.assign([1,2,3], {offset: 4});

I was considering:

interface Bar {
    [key: number]: number;
    offset: number;
}

But I still get errors when accessing Array prototypes (map/reduce/etc).

Upvotes: 0

Views: 44

Answers (1)

falinsky
falinsky

Reputation: 7428

It seems that you can have your interface Bar to be extending Array class:

const foo = Object.assign([1,2,3], {offset: 4});

interface Bar extends Array<Number> {
    offset: number;
}

function test(a: Bar) {
    console.log(a[0]);
    console.log(a.length);
    console.log(a.concat);
}

test(foo);

You can read more about Interfaces Extending Classes

UPDATE: In fact, you can create a separate type using intersections instead of creating a separate interface:

const foo = Object.assign([1,2,3], {offset: 4});

type Bar = number[] & {offset: number};

function test(a: Bar) {
    console.log(a[0]);
    console.log(a.length);
    console.log(a.concat);
}

test(foo);

Upvotes: 4

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