Node.js Errors

Node.js Errors

When building applications with Node.js, developers often come across different types of errors. Understanding these errors helps in writing cleaner, more reliable code. Broadly, Node.js applications encounter four categories of errors:

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1. Standard JavaScript Errors – Examples include <EvalError>, <SyntaxError>, <RangeError>, <ReferenceError>, <TypeError>, and <URIError>.
2. System Errors – Generated when an operating system-level issue occurs, such as file not found or network failure.
3. User-Specified Errors – Custom errors defined by developers for specific application logic.
4. Assertion Errors – Raised when an assertion test fails, often used in testing scenarios.

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Node.js Errors Example 1

Let’s start with a simple example of a standard JavaScript error: ReferenceError.

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File: error_example1.js

// Throws a ReferenceError because 'b' is undefined  
try {  
  const a = 1;  
  const c = a + b;  
} catch (err) {  
  console.log(err);  
}  

Now, open the Node.js command prompt and run:

node error_example1.js

This will throw a ReferenceError since variable b is not declared.

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Node.js Errors Example 2

Here’s an example demonstrating a system error using the fs module.

File: error_example2.js

const fs = require('fs');  

function nodeStyleCallback(err, data) {  
  if (err) {  
    console.error('There was an error', err);  
    return;  
  }  
  console.log(data);  
}  

fs.readFile('/some/file/that/does-not-exist', nodeStyleCallback);  
fs.readFile('/some/file/that/does-exist', nodeStyleCallback);  

To execute, run:

node error_example2.js

The first readFile call attempts to read a non-existent file and triggers a system error. The second call (if the file exists) will output its contents successfully.

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