Here are 10 perplexing questions, each accompanied by a code snippet. To enhance your learning experience, answers are concealed within a {% details 💣 Reveal %} tag—click 'Reveal' to uncover them. Let's dive in! 🚀
Each correct answer will get 10 points. What's your score? 👀
Comment Down.
1. What will be the output of the following code?
console.log(0.1 + 0.2 === 0.3);
Reveal
This occurs due to floating-point precision errors in JavaScript. The expression 💣 Reveal
false
0.1 + 0.2 results in 0.30000000000000004, which is not strictly equal to 0.3. Source
2. What does the following code output?
(function() {
var a = b = 5;
})();
console.log(b);
Reveal
In this code, 💣 Reveal
5
b is assigned to the global scope because var is only applied to a. Therefore, b becomes a global variable, accessible outside the function. Source
3. What will be the output of this code?
console.log(typeof null);
Reveal
This is a well-known bug in JavaScript. The 💣 Reveal
"object"
typeof operator returns "object" for null, even though null is not actually an object. Source
4. What does the following code print?
console.log([] + []);
console.log([] + {});
console.log({} + []);
console.log({} + {});
Reveal
These results are due to the type coercion and the way JavaScript handles the addition operator with different types. Source💣 Reveal
""
"[object Object]"
0
"[object Object][object Object]"
5. What will be the output of the following code?
console.log(1 < 2 < 3);
console.log(3 > 2 > 1);
Reveal
The first expression evaluates to 💣 Reveal
true
false
true because 1 < 2 is true, and true < 3 is also true. The second expression evaluates to false because 3 > 2 is true, and true > 1 is false. Source
6. What does the following code output?
console.log(typeof NaN);
7. What will be the output of this code?
let a = [1, 2, 3];
let b = [1, 2, 3];
console.log(a == b);
console.log(a === b);
Reveal
In JavaScript, arrays are compared by reference, not by value. Since 💣 Reveal
false
false
a and b are two different objects in memory, both comparisons return false. Source
8. What does the following code print?
console.log('5' - 3);
console.log('5' + 3);
Reveal
The subtraction operator converts the string 💣 Reveal
2
"53"
'5' to a number, resulting in 2. The addition operator concatenates the string '5' and the number 3, resulting in '53'. Source
9. What will be the output of the following code?
console.log(0 == false);
console.log(0 === false);
Reveal
The 💣 Reveal
true
false
== operator performs type coercion, so 0 is considered equal to false. The === operator checks for both value and type, so 0 and false are not strictly equal. Source
10. What does the following code output?
(function() {
console.log(1);
setTimeout(function(){ console.log(2) }, 1000);
setTimeout(function(){ console.log(3) }, 0);
console.log(4);
})();
Reveal
The code logs 💣 Reveal
1
4
3
2
1 and 4 immediately. The setTimeout with 0 delay is placed in the event queue and executed after the current stack is cleared, so 3 is logged next. Finally, the setTimeout with 1000 ms delay logs 2. Source
These questions delve into JavaScript's quirks and common pitfalls. Understanding them will enhance your problem-solving skills and prepare you for technical interviews. Happy coding! 🎉
For a more in-depth exploration of JavaScript interview questions, check out this comprehensive resource.
For a visual walkthrough of similar JavaScript interview questions, you might find this video helpful:
Top comments (3)
Makes me remember my first time with javascript :D Great content
I wonder how many answers you’ve gotten right?
Glad you liked it 😊. JavaScript can be a bit tricky, but it’s the backbone of the internet. Understanding the confusion is crucial for leading the industry.🤗