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assert.ok() function in Node.js
The assert module provides a bunch of different functionalities that are used for function assertion. The assert.ok tests whether the values are true or not. It will throw an assertion error if the value is not true.
Syntax
assert.ok(value, [message])
Parameters
The above parameters are described as below −
value – This parameter takes the value as input which will be checked by the assert ok() function.
message – This is an optional parameter. This is a user defined message printed when the function is executed.
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 – assertOK.js and copy the below code snippet. After creating the file use the below command to run this code.
node assertOk.js
assertOK.js
// Importing the module
const assert = require('assert').strict;
try {
//Checking the type of value
assert.ok(typeof 21 === 'number');
console.log("NO ERROR!")
} catch(error) {
console.log("Error: ", error)
}Output
C:\home
ode>> node assertOk.js NO ERROR!
Example
Let's take a look at one more example.
// Importing the module
const assert = require('assert').strict;
try {
//Checking the type of value
assert.ok(typeof 21 === 'string');
console.log("NO ERROR!")
} catch(error) {
console.log("Error: ", error)
}Output
C:\home
ode>> node assertOk.js Error: { AssertionError [ERR_ASSERTION]: The expression evaluated to a falsy value: assert.ok(typeof 21 === 'string') at Object. (/home/node/test/assert.js:6:9) 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: true, name: 'AssertionError [ERR_ASSERTION]', code: 'ERR_ASSERTION', actual: false, expected: true, operator: '==' }
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