`Record<Keys, Type>` in TypeScript

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`Record<Keys, Type>` in TypeScript

Alo's photo
Β·Apr 10, 2022Β·

2 min read

This article is part of the Series: Typescript utility types, in plain English

Record in a nutshell πŸ₯œ

Our first utility type uses two arguments:Keys and Type.

Record<Keys, Type> simply allows you to build an object type that has properties with keys Keys of values Type.

Sounds complex, but let me give you a very simple example:

type Television = Record<"sizeInInches", number>

/* is equal to
type Television = {
    "sizeInInches": number

let myBigTelevision:Television = {size: 23}

Example ✍️

Pretty simple, but why and when would we use this?

Like any other utility type, its real power comes when you combine them, as we will see later.

However, Record<Keys, Type> is useful to map a type to another type.

Let's say we are opening a television shop. Our Television definition above needs more refining. On top of the size we want to know:

  • if the TV is a smart TV or not,
  • if it's an OLED or an LCD,
  • if it has soundbars included,
  • the definition

We redefine our Television type.

type Television = {
    brand: string,
    model: string,
    isSmart: boolean,
    technology: "OLED" | "LCD",  // We could use an `enum` here
    hasSoundbars: boolean,
    definition: "HD" | "FHD" | "2k" | "4k" | "8k",

In our store, we have already a system to create and record product ID numbers. We would like to map our existing product ID system to our Television type such as:

const store = {
     'product_id_1': { brand: 'Sumsang', model: '2000fe', isSmart: true, /* other properties */},
     'product_id_2': /* another Television object */
     /* more product */

In that case, we are mapping a product ID to an existing type: the perfect tool for the job is Record<Keys, Type>:

type ProductID = string; 
// ☝️ Here it's a string, but it could be a number, an object containing the quantity, etc.

type Store = Record<ProductID, Television>
// πŸŽ‰ Our new `Store` type for our store in a single line.

Conclusion ☝️

Record<Keys, Type> is the perfect tool to map an existing type to a new one.

In our example, we created a new mapped type in a single line of code.

Combined with other utility types, it becomes a very versatile tool.

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