Expert Mastery — Series 2

Preview — 3 of 10 questions

What is the output?

javascript

const handler = {
  get(target, key) {
    return key in target ? target[key] : 37;
  },
};
const p = new Proxy({}, handler);
p.a = 1;
console.log(p.a, p.b);

A1 undefined

B1 37

Cundefined 37

DTypeError

Which statement about WeakRef is correct?

AA WeakRef prevents garbage collection of the referenced object.

BweakRef.deref() always returns the original object.

CA WeakRef allows the GC to collect the object; deref() returns undefined after collection.

DWeakRef is equivalent to a regular object reference.

What does the following print?

javascript

function* gen() {
  const x = yield 1;
  const y = yield x + 10;
  return x + y;
}

const g = gen();
console.log(g.next());
console.log(g.next(5));
console.log(g.next(3));

A{value:1,done:false} / {value:15,done:false} / {value:8,done:true}

B{value:1,done:false} / {value:10,done:false} / {value:5,done:true}

C{value:1,done:false} / {value:15,done:false} / {value:5,done:true}

D{value:undefined,done:false} / {value:15,done:false} / {value:8,done:true}

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