Check Object Equality

Introduction

In this lab, we will explore the concept of object equality in JavaScript. We will learn how to perform a deep comparison between two values to determine if they are equivalent using various techniques, such as checking if the values are identical, checking if they are non-object values with an equivalent value, and using Object.keys() to check if both values have the same number of keys. We will also understand how to use recursion to compare nested objects.

Skills Graph

How to Check Object Equality in JavaScript

To check if two values are equivalent, follow these steps:

1. Open the Terminal/SSH and type node to start practicing coding.
2. Perform a deep comparison between the two values using the equals() function.
3. Check if the two values are identical. If so, return true.
4. Check if both values are Date objects with the same time, using Date.prototype.getTime(). If so, return true.
5. Check if both values are non-object values with an equivalent value (strict comparison). If so, return true.
6. Check if only one value is null or undefined or if their prototypes differ. If so, return false.
7. If none of the above conditions are met, use Object.keys() to check if both values have the same number of keys.
8. Use Array.prototype.every() to check if every key in a exists in b and if they are equivalent by calling equals() recursively.

Use the following code to implement the equals() function:

const equals = (a, b) => {
  if (a === b) return true;

  if (a instanceof Date && b instanceof Date)
    return a.getTime() === b.getTime();

  if (!a || !b || (typeof a !== "object" && typeof b !== "object"))
    return a === b;

  if (a.prototype !== b.prototype) return false;

  const keys = Object.keys(a);
  if (keys.length !== Object.keys(b).length) return false;

  return keys.every((k) => equals(a[k], b[k]));
};

Use the following code examples to test the equals() function:

equals(
  { a: [2, { e: 3 }], b: [4], c: "foo" },
  { a: [2, { e: 3 }], b: [4], c: "foo" }
); // true

equals([1, 2, 3], { 0: 1, 1: 2, 2: 3 }); // true

Summary

Congratulations! You have completed the Check Object Equality lab. You can practice more labs in LabEx to improve your skills.