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

The assert module provides a set of assertion functions for verifying invariants. The assert.ifError() function throws value if value is not defined or null. When testing the error argument in callbacks, this function is very useful.
Syntax: 
 

assert.ifError(value)

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

  • value: This parameter holds the actual value. This value is thrown if value is not undefined or null. It is of any type.

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.ifError('error');
} 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]: ifError got unwanted exception: ‘error’
    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: false,
    code: ‘ERR_ASSERTION’,
    actual: ‘error’,
    expected: null,
    operator: ‘ifError’
    }

Example 2: Filename: index.js

javascript




// Requiring the module
const assert = require('assert').strict;
  
// Function call
try {
    assert.ifError(null);
    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_iferror_value

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