How to use stage 3 features in TypeScript?

Issue

Array.prototype.at() is currently a stage 3 proposal. I've tried setting "lib": ["ESNext"] in my tsconfig.json, but I still got:

Property 'at' does not exist on type 'number[]'.

So how to use Array.prototype.at() in TypeScript?

And to generalize, how to use stage 3 features in TypeScript?

TypeScript version is 4.3.5.

Solution

Currently, Array.prototype.at() support hasn't landed in TypeScript. To use it now, we need to install @types/proposal-relative-indexing-method and include the corresponding polyfill.

The same steps apply to the other stage 3 features if they're not already supported in TypeScript.

Answered By - Wenfang Du