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🚀 JavaScript Interview Questions with Answers — Part 4

31. What is if/else and switch?

Both are conditional statements used to make decisions in JavaScript.

if/else 
Executes code based on conditions. 

let age = 18;

if (age >= 18) {
    console.log("Adult");
} else {
    console.log("Minor");
}

switch 
Used when checking multiple possible values. 

let day = 2;

switch(day) {
    case 1:
        console.log("Monday");
        break;

    case 2:
        console.log("Tuesday");
        break;

    default:
        console.log("Invalid Day");
}

Difference: 
if/else - Better for conditions/ranges, Flexible 
switch - Better for exact values, Cleaner for many cases

32. What is the difference between for, for...in, and for...of?

for 
Traditional loop. 

for (let i = 0; i < 3; i++) {
    console.log(i);
}

for...in 
Used for iterating object keys. 

const person = {
    name: "Deepak",
    age: 25
};

for (let key in person) {
    console.log(key);
}

for...of 
Used for iterable values like arrays. 

const nums = [1, 2, 3];

for (let num of nums) {
    console.log(num);
}

Key Difference: 
Loop - Best For 
for - Full control 
for...in - Object properties 
for...of - Array values

33. What is the while and do-while loop?

Both loops execute code repeatedly while a condition is true.

while Loop 
Condition checked before execution. 

let i = 1;

while (i <= 3) {
    console.log(i);
    i++;
}

do-while Loop 
Runs at least once before checking condition. 

let i = 1;

do {
    console.log(i);
    i++;
} while(i <= 3);

Difference: 
while - Condition first, May run zero times 
do-while - Code first, Runs at least once

34. What is the ternary operator?

The ternary operator is a shorthand for if/else.

Syntax: 
condition? trueValue : falseValue

Example: 

let age = 20;

let result = age >= 18 ? "Adult" : "Minor";

console.log(result);

Benefits: 
• Shorter code
• Cleaner simple conditions

35. What is short-circuit evaluation?

JavaScript stops evaluating expressions as soon as the result is known.

Using && 
Returns first falsy value. 

console.log(false && "Hello");

Output: 
false

Using || 
Returns first truthy value. 

console.log("" || "Default");

Output: 
Default

Practical Example: 

let username = "";

let displayName = username || "Guest";

console.log(displayName);

36. What is the difference between break and continue?

Keyword - Purpose 
break - Stops the loop completely 
continue - Skips current iteration

break Example 

for (let i = 1; i <= 5; i++) {
    if (i === 3) {
        break;
    }
    console.log(i);
}

Output: 
1 
2

continue Example 

for (let i = 1; i <= 5; i++) {
    if (i === 3) {
        continue;
    }
    console.log(i);
}

Output: 
1 
2 
4 
5

37. How do you iterate over an array or object?

Array Iteration 
Using forEach() 

const nums = [1, 2, 3];

nums.forEach(num => {
    console.log(num);
});

Object Iteration 
Using for...in 

const person = {
    name: "Deepak",
    age: 25
};

for (let key in person) {
    console.log(key, person[key]);
}

Using Object.keys() 

Object.keys(person).forEach(key => {
    console.log(key);
});

38. How do you implement recursion?

Recursion is when a function calls itself until a stopping condition is met.

Example: Factorial

function factorial(n) {
    if (n === 1) {
        return 1;
    }
    return n * factorial(n - 1);
}

console.log(factorial(5));

Output: 
120

Important Parts: 
1. Base condition
2. Recursive call

Without a base condition → infinite recursion.

39. When would you use for vs forEach()?
for Loop vs forEach() 
for - More control, Can use break/continue, Faster in heavy loops 

forEach() - Cleaner syntax, Cannot stop early, Better readability

for Example

for (let i = 0; i < 3; i++) {
    console.log(i);
}

forEach() Example

[1, 2, 3].forEach(num => {
    console.log(num);
});

Interview Tip: 
Use forEach() for readability and for when more control is needed.

40. How do you handle early exits from loops?
Using break

for (let i = 1; i <= 5; i++) {
    if (i === 3) {
        break;
    }
    console.log(i);
}

Using return Inside Functions

function test() {
    for (let i = 1; i <= 5; i++) {
        if (i === 3) {
            return;
        }
        console.log(i);
    }
}

test();

Important:
forEach() does not support break directly.

Use:
• for
• for...of
• some()
• every()

for early exits.

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