Typescript map object to array with new objects, according to fields

Question

I have an object with some concrete fields:

 const obj1: Obj = {  
    hello: true, 
    second: false, 
    third: 311,  
    fifty: 50  
    .....  
}

I need to map some fields from this object to concrete number, (and use it value) and return array with it:

interface ArrayItem {
    index: number;
    visible: boolean;
}

// hello should be mapped to 3, and visible - 'true'
// result is:
const arr: ArrayItem[] = [{index: 3, visible: true}]

For concrete field. e.g. if obj1, has field "hello", result will be:

[  
    {
     index: 3  
     visible: (value of 'hello', so -> true)  
    }  
]

More examples:

 const obj1: Obj = {
    hello: true,
    second: false,
    third: 311,
    fifty: 50
    .....
}

// fields, which i looking:

const mapped = {
    hello: 3, // index value
    second: 5 // index value
}

output:

[
    {
     index: 3
     visible: (value of 'hello', so -> true)
    }
    {
     index: 5
     visible: (value of 'second', so -> false)
    }
]

So you want to parse Obj into new one only with index and visible keys, don't you? — Przemyslaw Jan Beigert
– Przemyslaw Jan Beigert, Commented Mar 20, 2019 at 15:16
that's correct. But depends on concrete fields. e.g. i know, that "hello" field will be transformed to 3. — trigger
– trigger, Commented Mar 20, 2019 at 15:18
Ok and how about Obj it must contains hello and second fields with booleans? And will any other keys affect on ArrayItem? — Przemyslaw Jan Beigert
– Przemyslaw Jan Beigert, Commented Mar 20, 2019 at 15:24
yes, they boolean. Obj has any other fields, which i do not need to handle. I have map with concrete fields which i need to map e.g. const maps = { hello: 3, second: 4 } — trigger
– trigger, Commented Mar 20, 2019 at 15:33

Przemyslaw Jan Beigert · Accepted Answer · 2019-03-21 16:30:12Z

1

Let's declare type definition of Obj

type Obj = { [key: string]: boolean };

Object with many key, and bool on all values.

Array items look like this:

interface ArrayItem {
    index: number;
    visible: boolean;
}

But we can get some more knowledge about types based on values from Obj. To declare that let's write InterfaceParser generic.

type InterfaceParser<T extends Obj> = {
  index: T['hello'] extends true ? 3 : number;
  visible: boolean;
}

T extends Obj means that input type must be at least Obj. extends true ? 3 : number means that when hello key is true the type of index is not number is 3.

Playground

Playground2

edited Mar 21, 2019 at 16:30

answered Mar 20, 2019 at 15:42

Przemyslaw Jan Beigert

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4 Comments

trigger Over a year ago

thanks @Przemyslaw Pietrzak, but seems its not what i need. I updated main topic, have a look please.

Przemyslaw Jan Beigert Over a year ago

To be honest i don't understand where is problem. I thought you want to have typed some values (e.g. 3 instead of number when 'hello'). Could you elaborate more, or give more exaples?

trigger Over a year ago

Updated topic. See below "More examples:" @Przemyslaw Pietrzak,

Przemyslaw Jan Beigert Over a year ago

I think you're looking for something like: click Playground2 link

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