Comment by DemocracyFTW2

Excuse me if I didn't get it right, but as a practical example, I'd assume that I can rewrite every program into JavaScript using the usual control structures and, beyond that, nothing but string values (which are immutable). Simple arithmetic would already be kind of a chore but can be done. (Input and output already happens only via serialized values (cf also webworkers) so there's that; for convenience use TypedArrays wrapped in classes that shield you from immutability). It is not obvious to me where `a = '[1,2]'; a1 = JSON.stringify( JSON.parse( a ).push( 3 ) ) );` is fundamentally different from just pushing a value to a copy of `a`. Also, you could write `a1 = a.slice(0,-1) + '3]'` which only uses non-mutating stuff under the hood.