This blog post lists language features that have been added to JavaScript and TypeScript since 2020. Each feature is illustrated with a short code example.

Quoting the blog post:

Rspack is a Rust-based JavaScript bundler developed by the ByteDance Web Infra team that has features including high-performance, webpack interoperability, flexible configuration etc.

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Rspack has completed the architecture of webpack loader. It means you can use all kinds of loaders in the community, such as babel-loader, less-loader, svgr etc. We are planning to support all features of loader in Rspack. By that time, you can use loaders which haven't been supported for now, such as vue-loader.

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Each let and const has a so-called temporal dead zone (TDZ): The time after entering its scope and before executing the declaration. During the TDZ, accessing the value of the variable throws an exception. The checks needed to enforce TDZs make let and const slower than var.

This document describes plans for V8 to omit TDZ checks when they aren’t necessary, thus making let and const faster.

The optimization was prompted by a discovery by the TypeScript team: Their compiler became almost 8% faster when they changed its code base and replaced all occurrences of let and const with var.