The post links to a TS issue [1] that explains > As of TypeScript 5.0, the project's output target was switched from es5 to es2018 as part of a transition to E

The post links to a TS issue [1] that explains > As of TypeScript 5.0, the project's output target was switched from es5 to es2018 as part of a transition to ECMAScript modules. This meant that TypeScript could rely on the emit for native (and often more-succinct) syntax supported between ES2015 and ES2018. One might expect that this would unconditionally make things faster, but surprise we encountered was a slowdown from using let and const natively! So they don't transpile to ES5, and that is the issue. 1: https://github.com/microsoft/TypeScript/issues/52924 https://github.com/microsoft/TypeScript/issues/52924