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

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)

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.
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