Node.js Assert Deep Strict Equal Method

The Node.js Assert module is a built-in module that provides a way to test values and objects in your code. Among its methods, the deepStrictEqual() method stands out as a powerful tool for performing deep comparisons between objects and arrays. This article will guide you through the basics of the assert.deepStrictEqual() method, including its syntax, parameters, return value, and practical examples to help beginners understand its utility.

1. Introduction

Comparison of complex data types in JavaScript is a common task that requires careful consideration, especially when dealing with deeply nested objects or arrays. The assert.deepStrictEqual() method is designed for this purpose, as it provides a way to compare the structure and values of objects or arrays rigorously.

2. Syntax

The syntax for the assert.deepStrictEqual() method is as follows:

assert.deepStrictEqual(actual, expected, [message])

3. Parameters

Parameter	Description
actual	The actual value to compare.
expected	The expected value to compare against.
message (optional)	A custom error message if the assertion fails.

4. Return Value

The assert.deepStrictEqual() method does not return any value. Instead, it throws an AssertionError if the assertion fails, providing feedback on the discrepancy.

5. Description

The deepStrictEqual() method performs a strict comparison between the actual and expected values. This means:

• Objects must have the same properties with the same values.
• Arrays must have the same elements in the same order.
• Types must be the same; for example, a string and a number are not equivalent.

6. Example

6.1 Using assert.deepStrictEqual() to Compare Objects

Let’s look at how to use assert.deepStrictEqual() to compare two objects:

const assert = require('assert');

const obj1 = { a: 1, b: { c: 2 } };
const obj2 = { a: 1, b: { c: 2 } };

try {
    assert.deepStrictEqual(obj1, obj2);
    console.log('Objects are strictly equal');
} catch (error) {
    console.error('Objects are not strictly equal:', error.message);
}

6.2 Using assert.deepStrictEqual() to Compare Arrays

Now, let’s see how the method works with arrays:

const assert = require('assert');

const array1 = [1, 2, [3, 4]];
const array2 = [1, 2, [3, 4]];

try {
    assert.deepStrictEqual(array1, array2);
    console.log('Arrays are strictly equal');
} catch (error) {
    console.error('Arrays are not strictly equal:', error.message);
}

7. Browser Support

The assert module is primarily designed for Node.js and is not available in a browser environment. For testing in the browser, consider exploring other libraries like Jasmine or Mocha.

8. Differences Between assert.deepStrictEqual() and assert.deepEqual()

Method	Description	Type Checking
assert.deepStrictEqual()	Compares the actual and expected values strictly.	Yes, checks both structure and type.
assert.deepEqual()	Compares the actual and expected values loosely.	No, performs type coercion.

For example:

const assert = require('assert');

const actual = { a: '1' };
const expected = { a: 1 };

try {
    assert.deepStrictEqual(actual, expected); // This will throw an error
    console.log('Strictly equal');
} catch (error) {
    console.error('Not strictly equal:', error.message);
}

assert.deepEqual(actual, expected); // This will not throw
console.log('Loosely equal');

9. Conclusion

The assert.deepStrictEqual() method is a crucial tool for developers who require precise and strict comparisons of objects and arrays in their testing strategy. Understanding how to use it effectively can lead to better debugging and more reliable code. It’s important to note the differences between this method and its looser counterpart, assert.deepEqual(), to choose the right one based on your comparison needs.

FAQ

What happens if the assertion fails?

When the assertion fails, assert.deepStrictEqual() throws an AssertionError, which includes details about the failure.

Can I use assert.deepStrictEqual in browsers?

No, this method is part of the Node.js assert module and is not available in browser environments.

Is assert.deepStrictEqual suitable for all types of comparisons?

It is best for comparing structured data types like objects and arrays. For simple value comparisons, you may use other assert methods.

How do I handle the AssertionError?

You can handle it using a try-catch block, as demonstrated in the examples above.