Subclassing Array

[backspaces]

I realize subclassing Array in the past was a no-no, but it works perfectly well with CoffeeScript, and has been quite useful and performant.

Is there a way 6to5 could allow subclassing Array (and other built-ins?). NOT at the cost of the beautiful code generation .. but if its just that browser foo doesn't support, I'd be OK with that. And as I recall, es6 explicitly says we can subclass builtins.

[sebmck]

This is more of a limitation on ES5 engines than 6to5. For example, the behaviour wouldn't be consistent or predictable across the different JavaScript engines, happy to be proven wrong however.

The following works on v8 but I'm not giving any guarantees that it'll work anywhere else:

class Foo extends Array {

}

var foo = new Foo;
foo.push("test");
foo; // { 0: "test", length: 1 }