It has some strange or weirdly specified features (ASI? HTML-like Comments?) and unusual features (prototype-based inheritance? a dynamically-bounded this?), but IMO it's a small language.
- Regular expressions - not just in the "standard library" but in the syntax.
- An entire module system with granular imports and exports
- Three different ways to declare variables, two of which create temporal dead zones
- Classes with inheritance, including private properties
- Dynamic properties (getters and setters)
- Exception handling
- Two different types of closures/first class functions, with different binding rules
- Async/await
- Variable length "bigint" integers
- Template strings
- Tagged template literals
- Sparse arrays
- for in/for of/iterators
- for await/async iterators
- The with statement
- Runtime reflection
- Labeled statements
- A lot of operators, including bitwise operators and two sets of equality operators with different semantics
- Runtime code evaluation with eval/Function constructor
And honestly it's only scratching the surface, especially of modern ECMAScript.
A language spec is necessarily long. The JS language spec, though, is so catastrophically long that it is a bit hard to load on a low end machine or a mobile web browser. It's on another planet.