util.isDeepStrictEqual() Method in Node.js

Node.js provides a range of utility functions through its Utility Module. One particularly useful method is util.isDeepStrictEqual(), which allows developers to compare two values deeply and strictly. This method goes beyond simple equality checks, ensuring that both structure and data types match between the values being compared.

What is util.isDeepStrictEqual()?

The util.isDeepStrictEqual() method checks whether two values are deeply equal and of the same type. It's ideal for comparing objects, arrays, or any nested data structures where exact matching is required, including their data types.

Syntax

util.isDeepStrictEqual(val1, val2)

- val1: The first value to compare.

- val2: The second value to compare.

The method returns true if both values are deeply and strictly equal; otherwise, it returns false.

Key Difference from Shallow Equality

While shallow comparisons only check references or top-level properties, util.isDeepStrictEqual() traverses nested structures and ensures both values have the same type and content at every level.

Basic Example

const util = require('util');

const a = { name: 'John', age: 25 };
const b = { name: 'John', age: 25 };

console.log(util.isDeepStrictEqual(a, b)); // true

In this example, even though a and b are two different objects in memory, their contents and types are identical, so the result is true.

Example with Different Types

console.log(util.isDeepStrictEqual(1, '1')); // false

Even though 1 and '1' have the same value when loosely compared, the method returns false because their types are different.

Nested Objects Example

const obj1 = { user: { id: 101, active: true } };
const obj2 = { user: { id: 101, active: true } };

console.log(util.isDeepStrictEqual(obj1, obj2)); // true

Here, both objects have nested structures with the same keys, values, and types. Hence, the result is true.

When to Use

• To verify data integrity in tests.
• When comparing deeply nested objects or arrays.
• For strict equality checks beyond what === can provide.

Conclusion

The util.isDeepStrictEqual() method in Node.js is a reliable way to perform deep and strict comparisons between values. It's especially useful in scenarios where accuracy and precision in data matching are critical, such as testing or validation tasks. By ensuring both structure and data type match exactly, this method helps write more robust and error-free code.