CODEWITHSUNDEEP
typescripttypescript-typings
Georgi Naumov
Georgi Naumov

Reputation: 4211

Converting object to union type

I have a question for typescript. I want to create somemething like union from a object values. How I can achieve this? eg: 

const x = {
    x: 1,
    y: 2,
    z: 'a string',
    k: document.createElement('div')
}

const y = (y: the value which exist of x ): boolean => {
  return true
}

Something like: 

type ValueOf<T> = T[keyof T];

but for objects. Any hints are welcome.

Upvotes: 3

Views: 7401

Answers (2)

Titian Cernicova-Dragomir
Titian Cernicova-Dragomir

Reputation: 250376

To get a union of the values in the type of a variable you can use ValueOf<typeof x>. For your example that type would be string | number | HTMLDivElement

const x = {
    x: 1,
    y: 2,
    z: 'a string',
    k: document.createElement('div')
}
type ValueOf<T> = T[keyof T]; 
const y = (P: ValueOf<typeof x>): boolean => { // p:  string | number | HTMLDivElement
   return true
}

From the comments you want the literal types (1 | 2 | "a string") not the base types. For this to work, you need to change the type pf x to include the literal types. The simplest way to do this is in 3.4 to add a const assertion:

const x = {
    x: 1,
    y: 2,
    z: 'a string',
    k: document.createElement('div')
} as const
type ValueOf<T> = T[keyof T];
const y = (p: ValueOf<typeof x>): boolean => { // p:  1 | 2 | "a string" | HTMLDivElement
    return true
}

Upvotes: 13

Tomasz Białecki
Tomasz Białecki

Reputation: 1121

I think this is what you need:

export const xx = {
    x: 1,
    y: 2,
    z: 'a string',
    k: document.createElement('div')
};

type ValueOf<T> = T[keyof T];

type XValues = ValueOf<typeof xx>;

Upvotes: 4

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