What is the notEqual method of the assert module in Node.js?

Note: You can view a list of rules for the != operator here.

To use the notEqual method, you will need to install the assert module using the command prompt, as shown below:

npm install assert

After the installation is complete, you will need to import the assert module into the program, as shown below:

const assert = require('assert');

The prototype of the notEqual method is shown below:

notEqual(actual, expected[, message])

Parameters

The notEqual method takes the following parameters:

actual: The first of the two values to compare.
expected: The second of the two values to compare.
message: This optional parameter holds the error message in case of an AssertionError. If this parameter is left empty, a default message is assigned.

Return value

If the values are equal, then the notEqual method throws an AssertionError, and the program terminates; otherwise, execution continues as normal.

In case of an error, the message property of the AssertionError is set equal to the message parameter. If the message parameter is not provided, a default value is assigned to the message property of the AssertionError.

Note: The notEqual method also handles NaN(Not-A-Number) comparisons. If both values are NaN, the notEqual method recognizes them as being identical.

Example

The code below shows how the notEqual method works in Node.js:

const assert = require('assert');
// evaluating first expression
try{
  assert.notEqual(10, 5, "Assertion Error: The values are equal.")
  console.log("No error.")
}
catch(error){
  console.log(error.message)
}
// evaluating second expression
try{
  assert.notEqual(10, 10, "Assertion Error: The values are equal.")
  console.log("No error.")
}
catch(error){
  console.log(error.message)
}
// evaluating third expression
try{
  assert.notEqual(10, "10", "Assertion Error: The values are equal.")
  console.log("No error.")
}
catch(error){
  console.log(error.message)
}

Explanation

The code above uses $3$ different expressions to show the behavior of the notEqual method.

In the first expression in line $5$ , the actual and expected parameters are not equal, so the notEqual method does not throw any errors. Therefore, only the try branch of the try-catch block executes.

In the second expression in line $14$ , the actual and expected parameters are both $10$ , so an error is thrown, which triggers the catch branch of the try-catch block. The code outputs the message associated with the error, i.e., the string provided as the message parameter to the notEqual method in line $14$ .

Similarly, in the third expression in line $23$ , the actual and expected parameters are both 10, but they have different types. The actual parameter is an integer, whereas the expected parameter is a string. Since the notEqual method uses abstract equality comparison rules, an error is thrown, which triggers the catch branch of the try-catch block. The code outputs the message associated with the error, i.e., the string provided as the message parameter to the notEqual method in line $23$ .

Free Resources