Final assessment

Twelve questions across the whole course. Score 70% or more to pass and unlock your certificate. You can retake it as often as you like.

Finish every lesson to earn the certificate — you can take the assessment any time.

What does console.log(typeof (450 + "50"), 450 - "50") print?

number 400
string 45050
string 400
number 500

What does [3, 1, 2].map((n) => n * 2).filter((n) => n > 2) return?

[6, 4]
[4, 6]
[6, 2, 4]
[3, 2]

An expense has no receipt property. Which expression throws?

expense.receipt?.url
expense?.receipt
expense.receipt ?? "none"
expense.receipt.url

In what order are the letters logged?

JavaScript

setTimeout(() => console.log("A"), 0);
(async () => {
  console.log("B");
  await null;
  console.log("C");
})();
console.log("D");

A B C D
B D C A
B C D A
D B C A

totalsByCategory uses reduce with {} as the initial value and throws Cannot read properties of undefined on the second expense. What is the most likely cause?

The initial value should be [], not {}.
The expenses must be sorted by category first.
reduce cannot build objects, only numbers.
The callback has braces but does not return totals, so the second call receives undefined.

Two parts of Pocket each call createIdGenerator("exp") and sometimes produce the same id. What is the right fix?

Store the counter in a global var instead.
Call createIdGenerator("exp") inside each click handler.
Create one generator in one module and import that same function wherever ids are needed.
Use Math.round(Math.random() * 10) as the id.

A labels list is rendered with li.innerHTML = `<b>${label}</b>`; and a user saves the label <img src=x onerror=alert(1)>. What is the safe fix?

Wrap the label in quotes inside the template.
Create the <b> with createElement and set its textContent to the label.
Use outerHTML instead of innerHTML.
Limit labels to 20 characters.

getJson returns a promise that rejects. What does safeLoad() do?

JavaScript

async function safeLoad() {
  try {
    return getJson("/api/rates");
  } catch {
    return {};
  }
}

It returns a promise that rejects, because without await the rejection happens after the try block has finished.
It resolves with {}.
It resolves with undefined.
It throws synchronously when called.

You need amounts sorted from largest to smallest for a chart, while another panel still shows amounts in its original order. Which line is right?

amounts.sort((a, b) => b - a)
amounts.toSorted()
[...amounts].sort()
amounts.toSorted((a, b) => b - a)

items.forEach(store.add); throws Cannot read properties of undefined (reading '#items') inside add. Which change fixes it?

Declare store with let instead of const.
Write items.forEach(store.add());.
Write items.forEach((item) => store.add(item));.
Assign const add = store.add; first and pass add.

The check if (amountInput.value == 0) is meant to catch an amount of zero. Why does it also run when the field is empty?

Empty number inputs contain the text “0”.
== converts "" to the number 0 before comparing, so "" == 0 is true.
value is null when the field is empty.
Number inputs return NaN when empty, and NaN == 0 is true.

What happens with JSON.parse(JSON.stringify({ when: new Date() })).when.getFullYear()?

It throws a TypeError, because when comes back as a string, which has no getFullYear method.
It returns the current year.
It returns NaN.
It returns undefined.

12 questions unanswered