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Post #3407
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๐ JavaScript Interview Questions with Answers โ 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.
switch
Used when checking multiple possible values.
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...in
Used for iterating object keys.
for...of
Used for iterable values like arrays.
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.
do-while Loop
Runs at least once before checking condition.
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:
Benefits:
โข Shorter code
โข 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.
Output:
false
Using ||
Returns first truthy value.
Output:
Default
Practical Example:
36. What is the difference between break and continue?
Keyword - Purpose
break - Stops the loop completely
continue - Skips current iteration
break Example
Output:
1
2
continue Example
Output:
1
2
4
5
37. How do you iterate over an array or object?
Array Iteration
Using forEach()
Object Iteration
Using for...in
Using Object.keys()
38. How do you implement recursion?
Recursion is when a function calls itself until a stopping condition is met.
Example: Factorial
Output:
120
Important Parts:
1. Base condition
2. Recursive call
Without a base condition โ infinite recursion.
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:
โข Shorter code
โข 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 โ infinite recursion.
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