Node.js Errors

Node.js Errors

When building applications with Node.js, developers often come across different types of errors. Understanding them helps you write cleaner, more reliable code. Broadly, Node.js applications encounter four categories of errors.

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Four Categories of Node.js Errors

• Standard JavaScript Errors: EvalError, SyntaxError, RangeError, ReferenceError, TypeError, URIError.
• System Errors: OS-level issues such as file not found or network failure.
• User-Specified Errors: Custom errors defined by developers for app logic.
• Assertion Errors: Raised when an assertion test fails, often in testing.

Example 1: ReferenceError (Standard JS Error)

// error_example1.js
try {
  const a = 1;
  const c = a + b; // b is not defined
} catch (err) {
  console.log(err);
}

// Run: node error_example1.js

Example 2: System Error (fs module)

// 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('/path/does-not-exist', nodeStyleCallback);

The first readFile call attempts to read a non-existent file and triggers a system error handled in the callback.

Error Handling Best Practices

• Always handle the err argument in callbacks.
• Use try...catch for synchronous code and .catch() for promises.
• Create custom error classes that extend Error for clearer messages.
• Never silently swallow errors ÔÇö log or rethrow them.

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