Question

187

How do I get the key of a value in a Typescript Record

rated 0 times [ 194] [ 7] / answers: 1 / hits: 78510 / 5 Years ago, tue, november 19, 2019, 12:00:00

Here's the code:

export type Period = 'dy' | 'wk' | 'mn' | 'qt' | 'yr';



const periods: Record<Period, string> = {

    dy: 'Day',

    wk: 'Week',

    mn: 'Month',

    qt: 'Quarter',

    yr: 'Year'

  };

When I try to do this:

const key = Object.keys(periods).find(key => periods[key] === 'Day');

I get an error of course, since periods[key] cannot guarantee that key is of the correct type. How should I really go about doing this? I thought of an enum but I can't do reverse lookups. All I'm trying to achieve is an input field that displays 'Day' but has a key of dy (etc.) and can set the state to the correct key and not the value when the user picks another value.

Answers

Only authorized users can answer the question. Please sign in first, or register a free account.

elians

Add To Favorites

Follow

Total Points: 417

Total Questions: 87

Total Answers: 101

Location: Barbados

Member since Sun, Nov 27, 2022

2 Years ago

answered 5 Years ago myakylas · Accepted Answer

Object.keys returns string[] not Array<keyof T> (where T is the type of the value passed in). The reasons for this are outlined here.

Since your object is probably not going to have unknown keys, you can use a type assertion:

export type Period = 'dy' | 'wk' | 'mn' | 'qt' | 'yr';



const periods: Record<Period, string> = {

  dy: 'Day',

  wk: 'Week',

  mn: 'Month',

  qt: 'Quarter',

  yr: 'Year'

};



const key = (Object.keys(periods) as Array<Period>).find(key => periods[key] === 'Day');

Playground Link