Node.js assert.fail() Function
The assert module provides a set of assertion functions for verifying invariants. The assert.fail() function throws an AssertionError with the provided the error message or with a default error message.
Syntax:
assert.fail([message])
Parameters: This function accepts following parameters as mentioned above and described below:
- 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:
- 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
// Requiring the module const assert = require( 'assert' ).strict; // Function call try { assert.fail(); } 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]: Failed
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: undefined,
expected: undefined,
operator: ‘fail’
}
Example 2: Filename: index.js
// Requiring the module const assert = require( 'assert' ).strict; // Function call try { assert.fail( new TypeError( 'My custom defined error' )); } 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: TypeError: My custom defined error
at Object.(C:\Users\Lenovo\Downloads\index.js:6:17)
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
Reference: https://nodejs.org/dist/latest-v12.x/docs/api/assert.html#assert_assert_fail_message
Contact Us