Node.js assert.notStrictEqual() Function

The assert module provides a set of assertion functions for verifying invariants. The assert.notStrictEqual() function tests strict inequality between the actual and the expected parameters. If the condition is true it will not produce an output else an assertion error is raised. 

Syntax:

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

Parameters: This function has three parameters, the actual parameter is of any type, the expected parameter is of any type and the message parameter can be of string or error type.

Return Value: This function returns an assertion error of object type.

Installation of assert module:

You can visit the link to Install the assert module. You can install this package by using this command.

npm install assert

Note: Installation is an optional step as it is an inbuilt Node.js module.

After installing the assert module, you can check your assert version in the command prompt using the command.

npm version assert

Project structure :

:

After that, you can create a folder and add a file, for example, index.js as shown below.

Example 1: In this example, we will see the use of the assert.notStrictEqual() Function

Filename: index.js

javascript

// Requiring the module
const assert = require('assert').strict;

let a = 2;
let b = 2;

// Function call
try {
    assert.notStrictEqual(a, b)
} catch (error) {
    console.log("Error: ", error)
}

Steps to run the program:

Run the index.js file using the below command:

node index.js

Output:

Error: AssertionError [ERR_ASSERTION]: Expected “actual” to be strictly unequal to: 2 at Object. (C:\Users\Lenovo\Downloads\index.js:9:12) at Module._compile (internal/modules/cjs/loader.js:1138:30) at Object.Module._extensions..js (internal/modules/cjs/loader.js:1158:10) at Module.load (internal/modules/cjs/loader.js:986:32) at Function.Module._load (internal/modules/cjs/loader.js:879:14) at Function.executeUserEntryPoint [as runMain] (internal/modules/run_main.js:71:12) at internal/main/run_main_module.js:17:47 { generatedMessage: true, code: ‘ERR_ASSERTION’, actual: 2, expected: 2, operator: ‘notStrictEqual’ }

Example 2: In this example, we will see the use of the assert.notStrictEqual() Function

Filename: index.js

javascript

// Requiring the module
const assert = require('assert').strict;

let a = 4;
let b = "Four";

// Function call
try {
    assert.notStrictEqual(a, b)
    console.log("No Error Occurred")
} catch (error) {
    console.log("Error: ", error)
}

a = 4;
b = 4;

// Function call
try {
    assert.notStrictEqual(a, b)
} catch (error) {
    console.log("Error Occurred: ", error)
}

Steps to run the program:

Run the index.js file using the below command: 

node index.js

Output:

No Error Occurred Error Occurred: AssertionError [ERR_ASSERTION]: Expected “actual” to be strictly unequal to: 4 at Object. (C:\Users\Lenovo\Downloads\index.js:20:12) at Module._compile (internal/modules/cjs/loader.js:1138:30) at Object.Module._extensions..js (internal/modules/cjs/loader.js:1158:10) at Module.load (internal/modules/cjs/loader.js:986:32) at Function.Module._load (internal/modules/cjs/loader.js:879:14) at Function.executeUserEntryPoint [as runMain] (internal/modules/run_main.js:71:12) at internal/main/run_main_module.js:17:47 { generatedMessage: true, code: ‘ERR_ASSERTION’, actual: 4, expected: 4, operator: ‘notStrictEqual’

Reference: https://nodejs.org/dist/latest-v12.x/docs/api/assert.html#assert_assert_notstrictequal_actual_expected_message