JavaScript snippets for Coding Interview

In this article, we will cover some JavaScript snippets that are commonly used in coding interviews. These snippets will help you solve coding problems more efficiently and effectively.

Table of Contents

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Arrays

Create & initialize an array

const arr = new Array(5).fill(0);
console.log(arr); // [0, 0, 0, 0, 0]

Create and initialize matrix

const rowsSize = 2;
const colsSize = 3;
let matrix = [...Array(rowsSize)].map(row => Array(colsSize).fill(0));  
console.log(matrix); // [[0, 0, 0], [0, 0, 0]]

Get subarray from array

Use arr.slice(leftIdx, rightIdx+1) approach

const arr = [1, 2, 3, 4, 5];
const subArr = arr.slice(1, 3);
console.log(subArr); // [2, 3]

Find max element in array

const arr = [1, 2, 3, 4, 5];
const max = Math.max(...arr);
console.log(max); // 5

Swap two numbers in array

const arr = [1, 2, 3, 4, 5]
console.log(arr) // [ 1, 2, 3, 4, 5 ]

// Swap two numbers at index 0 and 1
[arr[0], arr[1]] = [arr[1], arr[0]]
console.log(arr) // [ 2, 1, 3, 4, 5 ]

reduce() to calculate sum of array

reduce() is a function that takes two arguments, an accumulator and a currentValue, and returns a single value. It can be used to calculate the sum of an array.

const numbers = [1, 2, 3, 4, 5];

const sum = numbers.reduce((accumulator, currentValue) => {
  return accumulator + currentValue;
}, 0);

console.log(sum); // Output: 15

Strings

Reverse a string

To reverse a string, you can split the string into an array of characters, reverse the array, and then join the characters back into a string.

const str = 'hello';
const reversedStr = str.split('').reverse().join('');
console.log(reversedStr); // 'olleh'

Check if string is palindrome

const isPalindrome = (str) => {
    return str === str.split('').reverse().join('');
}

console.log(isPalindrome('hello')); // false
console.log(isPalindrome('madam')); // true

Count occurrences of a character in a string

const str = 'hello';
const char = 'l';
const count = str.split('').filter(c => c === char).length;
console.log(count); // 2

Sort String

To sort a string, you can split the string into an array of characters, sort the array, and then join the characters back into a string.

const str = 'hello';
const sortedStr = str.split('').sort().join('');
console.log(sortedStr); // 'ehllo'

Objects

Merge two objects

To merge two objects, you can use the spread operator (...) to create a new object with the properties of both objects.

const obj1 = { a: 1, b: 2 };
const obj2 = { b: 3, c: 4 };

const mergedObj = { ...obj1, ...obj2 };
console.log(mergedObj); // { a: 1, b: 3, c: 4 }

Check if object has a property

You can use the in operator to check if an object has a property.

const obj = { a: 1, b: 2 };

console.log('a' in obj); // true
console.log('c' in obj); // false

Get all keys of an object

You can use the Object.keys() method to get an array of all keys of an object.

const obj = { a: 1, b: 2, c: 3 };
const keys = Object.keys(obj);
console.log(keys); // ['a', 'b', 'c']

Iterate through Object

You can use for...in loop to iterate through the keys of an object.

const obj = { a: 1, b: 2, c: 3 };

for (const key in obj) {
    console.log(key, obj[key]);
}

Numbers

Generate random number in a range

const min = 1;
const max = 10;
const randomNum = Math.floor(Math.random() * (max - min + 1)) + min;
console.log(randomNum);

Convert Number to given base

const num = 10;
const base = 2;
const convertedNum = num.toString(base);
console.log(convertedNum); // '1010'

Map

Initialize Map

const map = new Map();
map.set('a', 1);
map.set('b', 2);
console.log(map); // Map { 'a' => 1, 'b' => 2 }

Iterate through Map

To iterate through a Map, you can use a for...of loop.

const map = new Map();
map.set('a', 1);
map.set('b', 2);

for (const [key, value] of map) {
    console.log(key, value);
}

Set

Initialize Set

const set = new Set();
set.add(1);
set.add(2);
console.log(set); // Set { 1, 2 }

Iterate through Set

To iterate through a Set, you can use a for...of loop.

const set = new Set();
set.add(1);
set.add(2);

for (const value of set) {
    console.log(value);
}

Adhoc

Check is given input a letter

To check if a given input is a letter you can use the following approach:

const isLetter = (value) => {
  return /^[a-zA-Z]$/.test(value);
}

console.log(isLetter('a')); // true
console.log(isLetter('B')); // true
console.log(isLetter('AB')); // false, more than one character
console.log(isLetter('')); // false, empty string
console.log(isLetter('*')); // false, wrong character

In the following code:

Capitalize given string

To capitalize given string, you can take first character of the string using charAt(0) and capitalize it with toUpperCase().

At the end concatenate it with the rest of the string using slice(1)

const capitalizeStr = (str) => {
  return str.charAt(0).toUpperCase() + str.slice(1);
}

console.log(capitalizeStr("hello")); // Output: "Hello"
console.log(capitalizeStr("world")); // Output: "World"

Convert Number to Letter

In this task we are required to convert given number to uppercase or lowercase letter.

Example:

1 -> A
2 -> B
3 -> C

or convert to lowercase letters

1 -> a
2 -> b
3 -> c

const numberToLetter = (num) => {
  // ASCII value of 'A' is 65, so we add (num - 1) to get the correct letter
  return String.fromCharCode(65 + (num - 1));
}

console.log(numberToLetter(1)); // Output: A
console.log(numberToLetter(2)); // Output: B
console.log(numberToLetter(26)); // Output: Z

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