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.
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); // 5Swap 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: 15Strings#
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')); // trueCount 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); // 2Sort 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); // falseGet 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'Split Number into Digits#
To split a number into its digits, you can convert the number to a string, split the string into an array of characters, and then map each character to a number.
const num = 12345;
const digits = num.toString().split('').map(Number);
console.log(digits); // [1, 2, 3, 4, 5]Swap two numbers#
To swap two numbers, you can use destructuring assignment.
let a = 1;
let b = 2;
[a, b] = [b, a];
console.log(a); // 2
console.log(b); // 1Map#
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]$/.test(value);
}
console.log(isLetter('a')); // true
console.log(isLetter('B')); // true
console.log(isLetter('AB')); // false, more than one character
console.log(isLetter('')); // false, empty string
console.log(isLetter('*')); // false, wrong characterIn the following code:
/.../these slashes indicate that everything between them is a regular expression pattern^asserts the start of the string[a-zA-Z]matches any single character in the range a-z or A-Z$asserts the end of the stringtest()method returns true if the input matches the pattern, false otherwise
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