🚀 JavaScript Interview Questions with Answers: Part-10

91. Write a function to find the sum of an array.

Using reduce()

function sumArray(arr) {
    return arr.reduce((total, num) => total + num, 0);
}

console.log(sumArray([1, 2, 3, 4]));

Output:
10

Using Loop

function sumArray(arr) {
    let sum = 0;

    for (let num of arr) {
        sum += num;
    }

    return sum;
}

92. Write a function to reverse a string.

Using split(), reverse(), join()

function reverseString(str) {
    return str.split("").reverse().join("");
}

console.log(reverseString("hello"));

Output:
olleh

Using Loop

function reverseString(str) {
    let reversed = "";

    for (let i = str.length - 1; i >= 0; i--) {
        reversed += str[i];
    }

    return reversed;
}

93. Write a function to find the largest number in an array.

Using Math.max()

function largestNumber(arr) {
    return Math.max(...arr);
}

console.log(largestNumber([2, 8, 5, 1]));

Output:
8

Using Loop

function largestNumber(arr) {
    let largest = arr[0];

    for (let num of arr) {
        if (num > largest) {
            largest = num;
        }
    }

    return largest;
}

94. Write a function to check if a string is a palindrome.
A palindrome reads same forward and backward.

Example:

function isPalindrome(str) {
    const reversed = str.split("").reverse().join("");
    return str === reversed;
}

console.log(isPalindrome("madam"));

Output:
true

Case-Insensitive Version

function isPalindrome(str) {
    str = str.toLowerCase();
    return str === str.split("").reverse().join("");
}

95. Write a function to remove duplicates from an array.

Using Set

function removeDuplicates(arr) {
    return [...new Set(arr)];
}

console.log(removeDuplicates([1, 2, 2, 3, 4, 4]));

Output:
[1, 2, 3, 4]

Using filter()

function removeDuplicates(arr) {
    return arr.filter((item, index) =>
        arr.indexOf(item) === index
    );
}

96. Write a function to implement debounce.
Debouncing delays execution until the user stops triggering events.

Example:

function debounce(fn, delay) {
    let timer;

    return function(...args) {
        clearTimeout(timer);

        timer = setTimeout(() => {
            fn.apply(this, args);
        }, delay);
    };
}

Usage:

``javascript
const search = debounce(() => {
console.log("Searching...");
}, 500);
``


Common Uses:
• Search bars
• Resize events
• Auto-save

97. Write a function to implement throttle.
Throttling limits execution frequency.

Example:

function throttle(fn, delay) {
    let lastCall = 0;

    return function(...args) {
        const now = Date.now();

        if (now - lastCall >= delay) {
            lastCall = now;
            fn.apply(this, args);
        }
    };
}

Usage:

``javascript
const scrollHandler = throttle(() => {
console.log("Scrolling...");
}, 1000);
``


Common Uses:
• Scroll events
• Mouse movement
• Window resizing

98. Write a function to flatten a nested array.

Using flat()

function flattenArray(arr) {
    return arr.flat(Infinity);
}

console.log(flattenArray([1, [2, [3, 4]]]));

Output:
[1, 2, 3, 4]

Recursive Solution

function flattenArray(arr) {
    let result = [];

    for (let item of arr) {
        if (Array.isArray(item)) {
            result = result.concat(flattenArray(item));
        } else {
            result.push(item);
        }
    }

    return result;
}