demonstration of the consequence of whether [[ConstructorKind]] is "base" or "derived"

consequence-of-constructor-kind-derived.js

// CLASS SYNTAX ////////////////////////////////////////////////////////////////

class AFoo {}
class ABar extends AFoo {}

// FUNCTION SYNTAX NEAR-EQUIV //////////////////////////////////////////////////

function BFoo() {
  if (!new.target) {
    throw new TypeError('Illegal constructor');
  }
}

function BBar() {
  if (!new.target) {
    throw new TypeError('Illegal constructor');
  } else {
    return Reflect.construct(BFoo, arguments, new.target);
  }
}

// OBSERVABLE DIFFERENCE ///////////////////////////////////////////////////////

let aInstanceInitializationCount = 0;
let bInstanceInitializationCount = 0;

Reflect.construct(ABar, [], new Proxy(function () {}.bind(), {
  get(target) {
    aInstanceInitializationCount++;
    return {};
  }
}));

Reflect.construct(BBar, [], new Proxy(function () {}.bind(), {
  get(target) {
    bInstanceInitializationCount++;
    return {};
  }
}));

console.log({
  aInstanceInitializationCount,
  bInstanceInitializationCount
});