JavaScript fundamentals practice set 1

Question 1

What does this print?
console.log(typeof null);

Accepted Answer

"object"

Question 2

What does this print?
console.log(0.1 + 0.2 === 0.3);

Accepted Answer

false

Question 3

What does this print?
console.log([1, 2, 3].map((x) => x * 2));

Accepted Answer

[ 2, 4, 6 ]

Question 4

What does this print?
console.log('5' + 3, '5' - 3);

Accepted Answer

53 2

Question 5

Which keyword declares a block-scoped variable that cannot be reassigned?

Accepted Answer

const

Question 6

What does this print?
const a = [1, 2, 3];
const b = a;
b.push(4);
console.log(a.length);

Accepted Answer

4

Question 7

What does this print?
console.log([10, 1, 3].sort());

Accepted Answer

[ 1, 10, 3 ]

Question 8

What is the output order?
console.log('A');
setTimeout(() => console.log('B'), 0);
Promise.resolve().then(() => console.log('C'));
console.log('D');

Accepted Answer

A D C B

Question 9

Which method creates a new array with only the elements that pass a test?

Accepted Answer

filter()

Question 10

What does this print?
console.log(null == undefined, null === undefined);

Accepted Answer

true false

Question 11

What does this print?
const { x = 5, y } = { y: 2 };
console.log(x + y);

Accepted Answer

7

Question 12

What does this print?
console.log([...'abc'].reverse().join(''));

Accepted Answer

cba

Question 13

What does JSON.parse('{"a":1}').a return?

Accepted Answer

1

Question 14

What does this print?
let n = 0;
for (let i = 0; i < 5; i++) { if (i === 3) continue; n += i; }
console.log(n);

Accepted Answer

7

Question 15

Which statement about arrow functions is true?

Accepted Answer

They do not have their own this

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