Table of contents Here are some examples of "as const" : Enum Types Tuple Types Function Return Types Object Properties Conclusion✨ Happy Coding 😊 you ever worked with types in and found yourself wanting more control over how those types behave? Well, there's a handy little feature called that can help with that. Have TypeScript as const is a way to make type checks stricter by preventing certain operations on a value. For example, let's say we have an array: as const const fruits = ['apple', 'banana', 'orange']; By default, TypeScript sees this as an array that can contain any string. But what if we wanted TypeScript to know that this array will ? only ever contain these three specific string values That's where comes in. By adding it, we make TypeScript treat the array in a more "specific" way: as const const fruits = ['apple', 'banana', 'orange'] as const; Now, instead of just being a , fruits are seen as the specific tuple type . string[] ['apple', 'banana', 'orange'] This means TypeScript will give us errors if we try to add or remove items from the array. It knows the values are "locked in". works on other types too. as const For example, you could mark an object as constant to prevent adding or removing properties: interface Cat {
  name: string;
  age: number;
}

const garfield = {
  name: 'Garfield', 
  age: 10
} as const; Now Garfield is seen as an object with very specific fields, rather than a loose Cat interface. Here are some examples of "as const" in action Here are some more examples of how can be used in TypeScript: as const Enum Types You can make an enum to remove the implicit number types: as const enum Colors {
  Red,
  Green,
  Blue
}

let c = Colors.Green; // number

enum ColorsAsConst {
  Red, 
  Green,
  Blue
} as const;

let c = ColorsAsConst.Green; // ColorsAsConst.Green Tuple Types Mark a tuple to make its types very specific: as const let tuple = [1, 'two'] as const;

tuple[0].toFixed(); // OK
tuple[1].toLowerCase(); // OK Function Return Types Mark a function return value to narrow its type: as const function createError() {
  return {message: 'an error'} as const;
}

const err = createError();
err.message = 'something else'; // Error Object Properties Objects marked prevent adding/removing properties: as const interface Point {
  x: number;
  y: number;
}

const p = {x: 0, y: 0} as const; 

p.z = 0; // Error So in summary, brings immutability and more precise types to enums, tuples, return values, objects, and more! as const Conclusion✨ In summary, const proves to be a clever tool for enforcing stricter and more specific types in TypeScript. It serves as a clear communication of your intent when you require values to remain immutable. Don't hesitate to implement it in your upcoming projects! Thank you for Reading this article💖 Also published here.

Walkthroughs, tutorials, guides, and tips. This story will teach you how to do something new or how to do something better.

Hot off the press! This story contains factual information about a recent event.

"as const" — Typescript's Unsung Hero for Strongly Typed Variables

About Author

Comments

TOPICS

THIS ARTICLE WAS FEATURED IN

Related Stories

Untitled Story

How to Use Tuples in TypeScript

10 More TypeScript Alternatives

The Noonification: What is a Support Vector Machine? (10/10/2022)

Getting Started With Software Development for Adobe Illustrator

289 Stories To Learn About Typescript

How to Use Tuples in TypeScript

10 More TypeScript Alternatives

The Noonification: What is a Support Vector Machine? (10/10/2022)

Getting Started With Software Development for Adobe Illustrator

289 Stories To Learn About Typescript

Light-Mode

Classic

Newspaper

Dark-Mode

Neon Noir

Minty

HN StartUps