Node.js – util Module

Node.js – util Module

The util module in Node.js provides utility functions that simplify and support core Node.js features, especially in asynchronous programming and debugging. It’s a built-in module and doesn’t require installation.

This module includes commonly used helper functions like promisify, format, types, and inherits.

Why Use the util Module?

• Convert callback-based functions to promises using util.promisify()
• Format console messages easily for debugging
• Inherit from one constructor to another (ES5-style classes)
• Deeply inspect objects while debugging
• Use built-in type-checking utilities

Importing the Util Module

1. util.promisify() – Convert Callback to Promise

Convert a Node-style callback function (error-first) into a promise-based one.

Example: Promisify fs.readFile()

2. util.format() – Format Strings Like printf

Output:

3. util.inherits() – Classical Inheritance (Pre-ES6)

Used when extending constructor functions before ES6 class syntax.

4. util.inspect() – Deep Object Inspection

Returns a string representation of an object (great for logging).

5. util.types – Type Checking Utilities

Real-World Use Cases

• Promisifying fs, child_process, or dns modules
• Formatting log messages for CLI or debug output
• Prototype-based class inheritance in legacy code
• Inspecting deeply nested objects while debugging
• Type checking in custom runtime utilities

Key Takeaways

• util provides utilities for debugging, formatting, inheritance, and async programming
• util.promisify() helps bridge callback APIs to async/await
• util.inspect() prints objects in developer-friendly formats
• It’s especially helpful for writing CLI tools, libraries, and diagnostics scripts