Javascript Quizzes You Can't Solve

Q1

console.log(018 - 015);
console.log("018" - "015");

Q2

const isTrue = true == []; 
const isFalse = true == ![]; 

console.log ( isTrue + isFalse);

Q3

console.log(3 > 2 > 1);

Q4

console.log(typeof typeof 1);

Q5

console.log(('b' + 'a' + + 'a' + 'a').toLowerCase());

Q6

console.log(typeof NaN);

Q7

console.log(0.1 + 0.2 == 0.3);

Q8

const numbers = [33, 2, 8];
numbers.sort();
console.log(numbers[1])

Conclusion

What percentage of the eight questions were correct?
If you get all of them right, please leave a comment!

Ref

• Javascript quizz
• The original article

Comments

[Jaydeep Pipaliya]

A1

1. 018 is treated as a decimal (18) since it is not a valid octal number, while 015 is a valid octal (13). So, 18 - 13 = 5.
2. "018" and "015" are converted to numbers 18 and 15. So, 18 - 15 = 3.

A2

• true == [] converts to 1 == 0, which is false. So, isTrue is false..
• true == ![] converts to true == false (1 == 0), which is false. So, isFalse is false.
• false + false is 0 + 0, which equals 0. So, console.log(isTrue + isFalse); will log 0.

A3

This will log false. Here's why:

• First, 3 > 2 evaluates to true.
• Then, true > 1 is evaluated. In JavaScript, true is converted to 1, so 1 > 1 evaluates to false.

A4
This will log "string". Here's why:

• typeof 1 returns "number".
• typeof "number" returns "string".

A5

This will log "banana". Here's why:

• 'b' + 'a' is 'ba'.
• + 'a' is NaN because 'a' cannot be converted to a number.
• 'ba' + NaN + 'a' results in 'baNaNa'.
• Calling .toLowerCase() on 'baNaNa' gives 'banana'.

A6

• This will log "number". NaN (Not-a-Number) is of type number in JavaScript.

A7

• This will log false. Due to floating-point precision issues, 0.1 + 0.2 does not exactly equal 0.3. Instead, it equals 0.30000000000000004.

A8

• This will log 33. The sort() method sorts the array elements as strings by default. Hence, the array becomes [2, 33, 8].

[Đặng Đình Sáng]

@itsjp

A1

An octal number is a number in JavaScript that has a leading zero.
018 is regarded as a decimal number, nevertheless, because it is an incorrect octal number. 015 is 13 in octal notation. 018-015 = 18-13 = 5 as a result.

A2

To begin with, allow me to clarify the first line: true and [] are changed to integers because they are of different kinds. First to be evaluated are number(true) and number([]), which are 1 and 0, respectively. const isTrue = false since 1 == 0.

Although true and ![] are both boolean values and are not converted to integers, it appears that the second line is the same. Additionally, ![] would be false because [] is understood to be true.
const isFalse = false and const isFalse = true are the results.

The final line, console.log (isTrue + isFalse); becomes console.log (false + false); as a result of the foregoing. console.log (0 + 0); becomes a number instead than false.
Therefore, the solution is 0.

[Jaydeep Pipaliya]

thank you for the corrections

[Syed Muhammad Ali Raza]

😔