Assert.ifError() method in Node.js

The assert module provides a set of assertion functions for verifying invariants. The assert.ifError() function throws if value is anything but null or undefined. This function is very useful when you want to test the error argument of a callback. The assert.ifError() function is another useful function provided by Node.js's assert module for writing tests. This particular approach tries to ascertain if a given value is either null or undefined. It raises an error if the passed value is not null or undefined. It is useful, especially when working with callback functions in asynchronous operations where the first argument is typically an error.

Syntax:

It has the following syntax:

Parameters: Several parameters of this function are as follows:

• Value: This argument includes the actual value. If this value isn't null or undefined, it raises an exception. It is found in all kinds.

Return Value:

This method returns a value that is an object-type assertion error.

Installation of an Assert Module:

• Installation is an optional step because of the integrated Node.js module.
• In the command prompt, use the command to confirm your assert version after installing the assert module.

Example 1:

Let us take an example to illustrate the Assert.ifError() function in Node.js.

Output:

 
Error occurred: AssertionError [ERR_ASSERTION]: ifError got unwanted exception: ENOENT: no such file or directory, open 'example.txt'
    at /index.js:17:12
    at ReadFileContext.callback (/index.js:7:5)
    at FSReqCallback.readFileAfterOpen [as oncomplete] (node:fs:314:13) {
  generatedMessage: false,
  code: 'ERR_ASSERTION',
  actual: [Error],
  expected: null,
  operator: 'ifError'   

Explanation:

Asynchronous Function:

• The readFileAsync function uses fs.readFile to read a file asynchronously.
• It accepts a callback function and filePath as input.

File read operation:

• The file at filePath is read by fs.readFile(filePath, 'utf8', (err, data) => {... }).
• If there was a problem reading the file, the callback gets an err; otherwise, it gets data.

Recall Management:

• A callback function called readFileAsync(filePath, (err, data) => {... }) is provided to handle the result of the file read operation.
• Within the callback, make an assertion. Use the function ifError(err) function to check whether an error is present.
• If err is an error object and assert an error.An assertion error is thrown by ifError(err), caught by the catch block, and logged as the error.

Example 2:

Let us take another example to illustrate the Assert.ifError() function in Node.js.

Output:

 
Connection refused. Please check the URL or your internet connection.   

Explanation:

Define function:

• Using http.get, fetchData sends an HTTP GET request.
• In addition to the URL input, it requires a callback function.

HTTP GET REQUEST:

• Use http.get(url, (response) => {... }) to send a GET request to the given URL.
• The broken response data is combined into a single string by concatenating it.
• The callback is initiated upon the completion of the response, yielding the resultant concatenated data and null as the error.
• If an error occurs, it is reported to the callback along with the request.

Managing Callbacks:

• The function fetchData(url, (err, data) => {...}) is offered as a callback to handle the HTTP request response.
• Assert is used inside the callback to identify errors.ifError(err).