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assert.ifError() function in Node.js
The assert module provides a bunch of different functionalities that are used for function assertion. Assert.ifError() function provides a functionality to throw an error if the value is not null or undefined. An error will be thrown if the value is not two of them.
Syntax
assert.ifError(value)
Parameters
The above parameters are described as below −
value – This paramter will hold the value to be checked for error. It will throw error in all cases except when the value is 'null' or 'undefined'.
Installing the Assert Module
npm install assert
The assert module is an inbuilt Node.js module, so you can skip this step as well. You can check the assert version using the following command to get the latest assert module.
npm version assert
Importing the module in your function
const assert = require("assert").strict;Example
Create a file with the name – assertIfError.js and copy the below code snippet. After creating the file use the below command to run this code.
node assertIfError.js
assertIfError.js
// Importing the module
const assert = require('assert').strict;
try {
assert.ifError('6');
// Will throw an error: value: 6
} catch(error) {
console.log("Error:", error)
}Output
C:\home
ode>> node assertIfError.js Error: { AssertionError [ERR_ASSERTION]: ifError got unwanted exception: '6' at Object. (/home/node/mysql-test/assert.js:5:9) at Module._compile (internal/modules/cjs/loader.js:778:30) at Object.Module._extensions..js (internal/modules/cjs/loader.js:789:10) at Module.load (internal/modules/cjs/loader.js:653:32) at tryModuleLoad (internal/modules/cjs/loader.js:593:12) at Function.Module._load (internal/modules/cjs/loader.js:585:3) at Function.Module.runMain (internal/modules/cjs/loader.js:831:12) at startup (internal/bootstrap/node.js:283:19) at bootstrapNodeJSCore (internal/bootstrap/node.js:623:3) generatedMessage: false, name: 'AssertionError [ERR_ASSERTION]', code: 'ERR_ASSERTION', actual: '6', expected: null, operator: 'ifError' }
We can see in the above example that that the value is not null or undefined.
Example
Let's take a look at one more example.
// Importing the module
const assert = require('assert').strict;
try {
assert.ifError(null);
console.log("No Error occured")
assert.ifError(undefined);
console.log("OK")
// Value: undefined & null is valid
} catch(error) {
console.log("Error:", error)
}Output
C:\home
ode>> node assertIfError.js No Error occured OK
We can see in the above example that the values are null and undefined which are valid values for ifError in assert.
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