How to specify a single kind of JavaScript object using Typescript

Question

How to specify a single kind of JavaScript object using Typescript

Let's say we have an object structured as follows:

const obj = [
  { createdAt: "2022-10-25T08:06:29.392Z", updatedAt: "2022-10-25T08:06:29.392Z"},
  { createdAt: "2022-10-25T08:06:29.392Z", animal: "cat"}
]

We want to develop a function that arranges the objects by the "createdAt" field, which is guaranteed to exist in each object. The function prototype would look like this:

export const sortArrayByCreatedAt = (arr: TypeArr) => {
    return arr.sort(function (a, b) {
        return new Date(b.createdAt).valueOf() - new Date(a.createdAt).valueOf();
    });
};

How should we define the type of the 'arr' parameter?

Type TypeArr {
  createdAt: string
}

Is it considered best practice to specify the type of the only known variable?

In my opinion, when someone else looks at this function, they might assume that the 'obj' array solely consists of objects with the 'createdAt' property. However, I couldn't come up with a better alternative.

javascript typescript

Answer 1

Answer №1

In my approach, I would define the TypeArr as an interface and implement the sort method as a generic function to maintain the existing return type.

export const sortArrayByCreatedAt = <T extends TypeArr>(arr: Array<T>) => {
    return arr.sort(function (a, b) {
        return new Date(b.createdAt).valueOf() - new Date(a.createdAt).valueOf();
    });
};

interface TypeArr{
    createdAt :string
}

const obj = [
  { createdAt: "2022-10-25T08:06:29.392Z", updatedAt: "2022-10-25T08:06:29.392Z"},
  { createdAt: "2022-10-25T08:06:29.392Z", animal: "cat"}
]

const sorted = sortArrayByCreatedAt(obj);

Interactive Playground

Answer 2

In my approach, I would define the TypeArr as an interface and implement the sort method as a generic function to maintain the existing return type.

export const sortArrayByCreatedAt = <T extends TypeArr>(arr: Array<T>) => {
    return arr.sort(function (a, b) {
        return new Date(b.createdAt).valueOf() - new Date(a.createdAt).valueOf();
    });
};

interface TypeArr{
    createdAt :string
}

const obj = [
  { createdAt: "2022-10-25T08:06:29.392Z", updatedAt: "2022-10-25T08:06:29.392Z"},
  { createdAt: "2022-10-25T08:06:29.392Z", animal: "cat"}
]

const sorted = sortArrayByCreatedAt(obj);

Interactive Playground

Answer 3

Answer №2

It appears that when passing the array to the function, you are also returning the same array. The current return type is TypeArr[], which does not accurately represent the additional properties within the objects.

To address this issue, I would suggest making the function sortArrayByCreatedAt generic.

export const sortArrayByCreatedAt = <T extends { createdAt: string }[]>(arr: T): T => {
    return arr.sort(function (a, b) {
        return new Date(b.createdAt).valueOf() - new Date(a.createdAt).valueOf();
    });
};

This modification ensures that the input type matches the return type.

Answer 4

It appears that when passing the array to the function, you are also returning the same array. The current return type is TypeArr[], which does not accurately represent the additional properties within the objects.

To address this issue, I would suggest making the function sortArrayByCreatedAt generic.

export const sortArrayByCreatedAt = <T extends { createdAt: string }[]>(arr: T): T => {
    return arr.sort(function (a, b) {
        return new Date(b.createdAt).valueOf() - new Date(a.createdAt).valueOf();
    });
};

This modification ensures that the input type matches the return type.

Answer 5

Answer №3

To incorporate optional properties in types or interfaces, you can simply add a question mark ? like this:

type MyType = {
    createdAt: string;
    updatedAt?: string;
    animal?: string;
}

interface MyInterface {
    createdAt: string;
    updatedAt?: string;
    animal?: string;
}

When typing an array of the object, use MyType[] or MyInterface[], for example:

export const sortArrayByCreatedAt = (arr: MyType[]) => {
    return arr.sort(function (a, b) {
        return new Date(b.createdAt).valueOf() - new Date(a.createdAt).valueOf();
    });
};

Answer 6

To incorporate optional properties in types or interfaces, you can simply add a question mark ? like this:

type MyType = {
    createdAt: string;
    updatedAt?: string;
    animal?: string;
}

interface MyInterface {
    createdAt: string;
    updatedAt?: string;
    animal?: string;
}

When typing an array of the object, use MyType[] or MyInterface[], for example:

export const sortArrayByCreatedAt = (arr: MyType[]) => {
    return arr.sort(function (a, b) {
        return new Date(b.createdAt).valueOf() - new Date(a.createdAt).valueOf();
    });
};

Answer 7

Answer №4

To create an interface with optional properties, simply add a question mark ? before the property name:

interface AnimalDetails {
  species: string
  habitat?: string
  diet?: string
}

Answer 8

To create an interface with optional properties, simply add a question mark ? before the property name:

interface AnimalDetails {
  species: string
  habitat?: string
  diet?: string
}

How to specify a single kind of JavaScript object using Typescript

Answer №1

Answer №2

Answer №3

Answer №4

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