How do you compare two objects for equality in JavaScript?

In JavaScript, comparing two objects for equality can be a bit nuanced. The `==` and `===` operators are used for equality comparison, but they behave differently when it comes to objects.

1. Shallow Equality:

   - The `==` and `===` operators perform a shallow equality check for objects. They compare references, not the content of the objects.

   - Two objects are considered equal with `==` or `===` only if they reference the exact same object.

   Example:

   let obj1 = { key: 'value' };

   let obj2 = { key: 'value' };

   let obj3 = obj1;

   console.log(obj1 == obj2);  // Output: false

   console.log(obj1 === obj2); // Output: false

   console.log(obj1 === obj3); // Output: true (same reference)

   In this example, `obj1` and `obj2` have the same structure, but they are different objects, so `==` and `===` return `false`. However, `obj1` and `obj3` reference the same object, so `===` returns `true`.

2. Deep Equality:

   - If you need to check if the content of two objects is equal (i.e., a deep equality check), you might need to implement a custom comparison function or use a library that provides deep equality comparison.

   - Libraries like Lodash provide a `_.isEqual()` function that performs a deep comparison.

   Example using Lodash:

   const _ = require('lodash');

   let obj1 = { key: 'value', nested: { innerKey: 'innerValue' } };

   let obj2 = { key: 'value', nested: { innerKey: 'innerValue' } };

   console.log(_.isEqual(obj1, obj2)); // Output: true (deep equality)

  

In this example, `_.isEqual()` compares the content of `obj1` and `obj2` recursively, and it returns `true` because the content is the same.

Keep in mind that when dealing with complex objects and nested structures, a deep equality comparison can become computationally expensive. Always consider the specific requirements of your use case and choose the appropriate method for comparing objects based on whether you need a shallow or deep comparison.