Node.js assert.doesNotMatch() Function

The assert module provides a set of assertion functions for verifying invariants. The assert.doesNotMatch() function expects the string input not to match the regular expression. If the condition is true it will not produce an output else an assertion error is raised. 

Syntax:

assert.doesNotMatch(string, regexp[, message])

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

• string: This parameter holds the string that need to be evaluated.
• regexp This parameter holds the regular expression which is matched.
• message This parameter holds the error message of string or error type. It’s an optional parameter.

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

Installation of assert module:

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

npm install assert

• Note: Installation is an optional step as it is inbuilt Node.js module.
• After installing the assert module, you can check your assert version in command prompt using the command.

npm version assert

• 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.doesNotMatch('I will try to pass', /fail/);
    console.log("No Error Occurred")
} catch(error) {
    console.log("Error:", error)
}

Steps to run the program:

• The project structure will look like this:
• Run index.js file using below command:

node index.js

Output:

No Error Occurred

Example 2: Filename: index.js

javascript

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

// Function call
try {
    assert.doesNotMatch('I will try to pass', /pass/);
    //console.log("No Error Occurred")
} catch(error) {
    console.log("Error:", error)
}

Steps to run the program:

• The project structure will look like this:
• Run index.js file using below command:

node index.js

Output:

Error: AssertionError [ERR_ASSERTION]: The input was expected to not match the 
regular expression /pass/. Input:

'I will try to pass'

    at Object. (C:\Users\Lenovo\Downloads\index.js:6:12)
    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: 'I will try to pass',
  expected: /pass/,
  operator: 'doesNotMatch'
}

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