Paul Cowan
Mar 9, 2023 ⋅ 6 min read

A complete guide to const assertions in TypeScript

Paul Cowan Contract software developer.

Recent posts:

Using ElectricSQL to build a local-first application

ElectricSQL is a cool piece of software with immense potential. It gives developers the ability to build a true local-first application.

Rahul Padalkar
Dec 1, 2023 ⋅ 11 min read
Using Rust And Leptos To Build Beautiful Declarative User Interfaces

Using Rust and Leptos to build beautiful, declarative UIs

Leptos is an amazing Rust web frontend framework that makes it easier to build scalable, performant apps with beautiful, declarative UIs.

Eze Sunday
Nov 30, 2023 ⋅ 10 min read
5 Best JavaScript Multi-Dimensional Array Libraries

5 best JavaScript multidimensional array libraries

Learn more about the 5 best JavaScript libraries for dealing with multidimensional arrays, such as ndarray, math.js, and NumJs.

Pascal Akunne
Nov 30, 2023 ⋅ 4 min read
Dom Scandinaro Leader Spotlight

Leader Spotlight: Leading by experience with Dom Scandinaro

We spoke with Dom about his approach to balancing innovation with handling tech debt and to learn how he stays current with technology.

Jessica Srinivas
Nov 30, 2023 ⋅ 6 min read
View all posts

5 Replies to "A complete guide to <code>const</code> assertions in TypeScript"

  1. The example in your conclusion is wrong: z and a would not be read-only since those are the keys for nested object. This is currently the behavior of “as const” syntax.

  2. that isn’t true, this is the resultant type:

    let obj: {
    readonly x: 10;
    readonly y: readonly [20, 30];
    readonly z: {
    readonly a: {
    readonly b: 42;
    and this error happens when you try to modify z o a
    Cannot assign to ‘z’ because it is a read-only property.(2540)

  3. The example with redux actions is striking. With interfaces it’s clear and reads nicely, with ‘const’ assertion, it becomes more…implicit and easier to overlook. IMO interfaces are better for this purpose. The goal is not to write maintainable code, not as little code as possible.
    But the purpose of the assertion is clear when it comes to literals.
    Nice article, thanks!

Leave a Reply