Off the top of my head, features that are entirely syntactical transformations and don't need a runtime: - Classes (except inheritance requires a tiny shim fun

Off the top of my head, features that are entirely syntactical transformations and don't need a runtime: - Classes (except inheritance requires a tiny shim function) - Destructuring (except destructuring iterators) - Rest parameters - Arrow functions - Shorthand object literals - Computed properties - Template strings (although tagged template strings require a non-trivial amount of shimming to mimic) - let and const (check correctness before transpiling, then compile to var. Transformation is non-trivial when inside loops, etc.) - Modules Features that do require a runtime / library: - Iterators and generators - Promises - Symbols - New ES6 methods on Object, Number, String, etc. (like Number.isNaN)