5 Javascript coding interview questions - Part 7

5 Javascript coding interview questions - Part 6

Q1. Flatten a Nested Object
Write a function that takes a nested object and flattens it into a single-level object with dot-separated keys.

Ans:

function flattenObject(obj, parent = '', res = {}){
  for(let key in obj){
    let newKey = parent ? `${parent}.${key}` : key;
    if(typeof obj[key] === 'object' && obj[key] !== null && !Array.isArray(obj[key])){
      flattenObject(obj[key], newKey, res);
    } 
   else{
      res[newKey] = obj[key];
    }
  }
  return res;
}

// Example
const input = { a: 1, b: { c: 2, d: { e: 3 } } };
console.log(flattenObject(input)); 
// { a: 1, "b.c": 2, "b.d.e": 3 }

Q2. Debounce Function
Implement a debounce function to delay execution until after a pause in calls.

Ans:

function debounce(fn, delay){
  let timeout;
  return function (...args) {
    clearTimeout(timeout);
    timeout = setTimeout(() => fn.apply(this, args), delay);
  };
}

// Example
const log = debounce(() => console.log("Debounced!"), 1000);
log();
log();
log(); // Only runs once after 1s

Q3. Throttle Function
Implement a throttle function to limit execution of a function to once every X milliseconds.

Ans:

function throttle(fn, limit) {
  let lastCall = 0;
  return function (...args) {
    const now = Date.now();
    if (now - lastCall >= limit) {
      lastCall = now;
      fn.apply(this, args);
    }
  };
}

// Example
const log = throttle(() => console.log("Throttled!"), 2000);
setInterval(log, 500); // Runs every 2s, not every 0.5s

Q4. Group Anagrams
Given an array of strings, group words that are anagrams of each other.

Ans:

function groupAnagrams(words) {
  const map = {};
  for (let word of words) {
    const key = word.split('').sort().join('');
    if (!map[key]) map[key] = [];
    map[key].push(word);
  }
  return Object.values(map);
}

// Example
console.log(groupAnagrams(["eat", "tea", "tan", "ate", "nat", "bat"]));
// [["eat","tea","ate"], ["tan","nat"], ["bat"]]

Q5. Currying Function
Implement a function that transforms a normal function into a curried one.

Ans:

function curry(fn) {
  return function curried(...args) {
    if (args.length >= fn.length) {
      return fn.apply(this, args);
    } else {
      return function (...nextArgs) {
        return curried.apply(this, args.concat(nextArgs));
      };
    }
  };
}

// Example
function add(a, b, c) {
  return a + b + c;
}

const curriedAdd = curry(add);
console.log(curriedAdd(1)(2)(3)); // 6
console.log(curriedAdd(1, 2)(3)); // 6

5 Javascript coding interview questions - Part 6