Deep Equal of two objects

Given two objects, determine if they are equal.

A deep equal is a process in which the entire object is compared to another object, including all nested objects and their properties.

function deepEqual(objA, objB) {
  // your code here
}

Example of usage

const a = { name: 'Tim', skills: ['JS', 'React'] };
const b = { name: 'Tim', skills: ['JS', 'React'] };

console.log(isEqual(a, b)); // true 

Approach 1: Using JSON.stringify

const isEqual = (a, b) => {
  return JSON.stringify(a) === JSON.stringify(b);
};

Approach 2: Using Recursion

This is the preferred approach that Interviewers are looking for. Hovewer, it's important to mention other possible approaches.

Here is the key points to consider:

• Handle strict equality and primitive types with ===
• Handle null and undefined
• Handle non-object types
• Handle different number of keys
• Handle circular references
• Handle Arrays with recursive element checking
• Handle Dates objects comparison with Date.prototype.getTime
• Handle Objects comparison with key-by-key recursive checking

Implementation:

const isEqual = (a, b) => {
  // Handle strict equality and primitive types  
  if (a === b) return true;

  // handle null and undefined
  if (a === null || b === null) return false;
  
  // handle non-object types
  if (typeof a !== 'object' || typeof b !== 'object') return false;
  
  const keysA = Object.keys(a);
  const keysB = Object.keys(b);

  // handle different number of keys
  if (keysA.length !== keysB.length) return false;
  
  // compare each key recursively   
  for (let key of keysA) {
    if (!keysB.includes(key)) return false;
    if (!isEqual(a[key], b[key])) return false;
  }

  return true;
};

Summary

• Deep equal is a process in which the entire object is compared to another object, including all nested objects and their properties.
• There are several approaches to implement deep equal.
  • The best approach is to use lodash isEqual.
  • The second best approach is to use recursion.
  • The worst approach is to use JSON.stringify.