Acessing type as object or Array in Typescript

Question

I am new to typescript.

I have a class Like this

class Document {
  constructor (data, id) {
    this.data = data
    this.id = id
  }
}

Here I know that Id is going to be String but data is going to be either object or array.

Can someone help me in figuring out what is going to be the interface for it.

[Update:] What have I tried?

I created an interface like this

interface Documents {
  data: Array | Object,
  id: Number
}

but this gives following error (red underline below array)

Generic type 'Array' requires 1 type argument(s).

If it makes any difference, I expect my array to be either empty or contain list of objects

Have you tried doing it like this: constructor (data: object | Array<any>, id: string)? — Sebastian Kaczmarek
– Sebastian Kaczmarek, Commented Jan 17, 2020 at 7:29
@SebastianKaczmarek Updated the question. Can we use interface and if yes then how? — Alwaysblue
– Alwaysblue, Commented Jan 17, 2020 at 7:34
notation like number[], string[] looks more easy for me. Also, when you read them they can be read as "number array" or "string array" — canbax
– canbax, Commented Jan 17, 2020 at 7:54

w08r · Accepted Answer · 2020-01-17 07:41:04Z

3

You need to specify the underlying type of array, as Array is a type constructor. I would err towards primitive types where possible. Also, if your data is either an object, an empty array, or a list of objects, I would keep simple and just define it as a (possibly empty) list of objects. So you might end up with something like this:

type DocData = [object]
interface DocumentInterface {
  data: DocData
  id: number
}

class Doc implements DocumentInterface {
    data: DocData
    id: number

    constructor (data: DocData, id: number) {
        this.data = data
        this.id = id
    }
}

answered Jan 17, 2020 at 7:41

w08r

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Comments

hoangdv · Accepted Answer · 2020-01-17 07:51:54Z

1

You can make Documents become a generic interface, your data need to be an array or a object, what is type of data you store in the array?, or what is type of the object? The type can be something, like User, Store...

Example:

interface Documents<T extends object> {
  data: Array<T> | T;
  id: number; // best practice: https://www.typescriptlang.org/docs/handbook/declaration-files/do-s-and-don-ts.html 
}

And you have another type like:

interface IUser {
  name: string,
  email: string,
}

Now you need to create a document with data is a IUser:

const doc: Documents<IUser> = {
  id: 1,
  data: {
    name: 'Tom',
    email: '[email protected]'
  }
}

or data will store many IUser:

const docs: Documents<IUser> = {
  id: 1,
  data: [{
    name: 'Tom',
    email: '[email protected]'
  }]
}

answered Jan 17, 2020 at 7:51

hoangdv

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2 Comments

Alwaysblue Over a year ago

the type of the data in the array isn't consistent

hoangdv Over a year ago

@anny123 How about Documents<any>, you can store anything to the array.

SDEZero · Accepted Answer · 2020-01-17 07:32:02Z

0

class Document {
    private data: [] | object;
    private id: string;
  constructor (data: [] | object, id:string) {
    this.data = data
    this.id = id
  }
}

answered Jan 17, 2020 at 7:32

SDEZero

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2 Comments

SDEZero Over a year ago

I'm not sure if Document is reserved keyword, you might need to lookup

Alwaysblue Over a year ago

Updated the question. Can we use interface and if yes then how?

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