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Node.js assert.deepStrictEqual() Function
  • Last Updated : 07 Aug, 2020

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

Syntax: 

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

Parameters: This function accepts the following parameters as mentioned above and described below: 

  • actual: This parameter holds the actual value that need to be evaluated. It is of any type.
  • expected: This parameter holds the expected value which is matched against actual value. It is of any type.
  • message: This parameter holds the error message of string or error type. It is an optional parameter.

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

Installation of assert module: 



  1. You can visit the link to Install assert module. You can install this package by using this command. 
    npm install assert
  2. Note: Installation is an optional step as it is inbuilt Node.js module. 
  3. After installing the assert module, you can check your assert version in command prompt using the command. 
    npm version assert
  4. After that, you can just create a folder and add a file for example, index.js as shown below.

    Example 1: Filename: index.js 
     

    javascript




    // Requiring the module
    const assert = require('assert').strict;
         
    // Function call
    try {
        assert.deepStrictEqual({ a: '5' }, { a: '5' });
    } catch(error) {
        console.log("Error: ", error)
    }

    Steps to run the program: 
     

    1. The project structure will look like this: 
       
    2. Run index.js file using below command: 
       
      node index.js
    3. Output: 
       

      Error:  AssertionError [ERR_ASSERTION]: Expected values to be strictly deep-equal:
      + actual – expected

       {
      +   a: 1
      –   a: ‘1’
       }
         at Object. (C:\Users\Lenovo\Downloads\index.js:14:12)
         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: [Object],
       expected: [Object],
       operator: ‘deepStrictEqual’
      }

    Example 2: Filename: index.js 
     

    javascript




    // Requiring the module
    const assert = require('assert').strict;
           
    // Function call
    try {
        assert.deepStrictEqual({ a: '5' }, { a: '5' });
        console.log("No Error Occured")
    } catch(error) {
        console.log("Error: ", error)
    }

    Steps to run the program: 
     

    1. The project structure will look like this: 
       
    2. Run index.js file using below command: 
       
      node index.js
    3. Output: 
       
      No Error Occured

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

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