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What is the assert.isNull() method in Chai.js?

Theodore Kelechukwu Onyejiaku

Grokking Modern System Design Interview for Engineers & Managers

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Overview

In Chai.js, assert.isNull() is used to check if a value is null or not.

It returns an error if the value passed is not null, and it returns nothing if the value passed is null.

Syntax

assert.isNull(val)
Syntax for assert.isNulll() nethod in Chai.js

Parameters

val: This is the value we want to check.

Return value

If the test succeeds, it returns. If the test fails, it returns an error.

Example

// import the chai module and assert interface
const {assert} = require('chai')
// function to check if values are null
const checkIfNull= (val1, val2) =>{
try{
// use the isNull() method
assert.isNull(val1)
}catch(error){
console.log(error.message)
}
}
checkIfNull(true)
checkIfNull(false)
checkIfNull(null) // test succeeded
checkIfNull(undefined)
checkIfNull(0)
Using the isNull() method in Chai.js

Explanation

  • Line 2: We import the chai module as well as the assert.isNull() method.
  • Line 5–12: We create a function that runs the test using the assert.isNull() method. It takes the value we want to check if they are null. We use the try/catch block to catch any errors if the test fails.
  • Lines 14–18: We invoke the function and pass some values to test if they are null.

    RELATED TAGS

    chai

    Grokking Modern System Design Interview for Engineers & Managers

    Ace your System Design Interview and take your career to the next level. Learn to handle the design of applications like Netflix, Quora, Facebook, Uber, and many more in a 45-min interview. Learn the RESHADED framework for architecting web-scale applications by determining requirements, constraints, and assumptions before diving into a step-by-step design process.

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