Frameworks like Ember and Glimmer are constantly attempting to walk a fine line between runtime performance and developer ergonomics. If we lean too heavily towards developer ergonomics we ship a bunch of extra code which hurts runtime performance, but if we lean too much in the direction of runtime performance

From the time that Ember CLI first started supporting transpilation of ES2015 (known as ES6 or ESNext back then), source could be authored in the latest ES version and the tooling would emit code that is ES5 compatible. Being able to author using the current spec version but support older