7 interview questions about Javascript programming

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How would you reverse a string in JavaScript?

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

How would you check if a given number is a prime number in JavaScript?

function isPrime(num) {
  if (num <= 1) {
    return false;
  }
  for (let i = 2; i < num; i++) {
    if (num % i === 0) {
      return false;
    }
  }
  return true;
}

How would you find the missing number in an array of consecutive integers?

function findMissingNumber(arr) {
  let sum = 0;
  let expectedSum = (arr.length + 1) * (arr[0] + arr[arr.length - 1]) / 2;
  for (let i = 0; i < arr.length; i++) {
    sum += arr[i];
  }
  return expectedSum - sum;
}

How would you implement a binary search algorithm in JavaScript?

function binarySearch(arr, target) {
  let left = 0;
  let right = arr.length - 1;
  while (left <= right) {
    let mid = Math.floor((left + right) / 2);
    if (arr[mid] === target) {
      return mid;
    } else if (arr[mid] < target) {
      left = mid + 1;
    } else {
      right = mid - 1;
    }
  }
  return -1;
}

How would you implement a breadth-first search algorithm in JavaScript?

function breadthFirstSearch(root, target) {
  let queue = [root];
  while (queue.length > 0) {
    let node = queue.shift();
    if (node.value === target) {
      return node;
    }
    for (let i = 0; i < node.children.length; i++) {
      queue.push(node.children[i]);
    }
  }
  return null;
}

How would you find the longest common prefix in an array of strings?

function longestCommonPrefix(strs) {
  if (strs.length === 0) {
    return '';
  }
  let prefix = strs[0];
  for (let i = 1; i < strs.length; i++) {
    while (strs[i].indexOf(prefix) !== 0) {
      prefix = prefix.substring(0, prefix.length - 1);
      if (prefix === '') {
        return '';
      }
    }
  }
  return prefix;
}

How would you merge two sorted arrays into one sorted array in JavaScript?

let arr1 = [1, 3, 5, 7];
let arr2 = [2, 4, 6, 8];

let mergedArr = arr1.concat(arr2);
mergedArr.sort((a, b) => a - b);