Node.js Tutorial - Node.js util Module

The util module contains a number of useful functions.

We can access the util module using a require('util') call.

To log out something to the console with a timestamp, you can use the util.log function.

var util = require('util'); 
util.log('sample message'); 

The code above generates the following result.


util.format function is similar to the C/C++ printf function.

The first argument is a string that contains zero or more placeholders.

Each placeholder is then replaced using the remaining arguments based on the meaning of the placeholder.

Popular placeholders are %s (used for strings) and %d (used for numbers).

var util = require('util'); 
var name = 'CSS'; 
var a = 33; 

console.log(util.format('%s has %d attributes', name, a)); 

The code above generates the following result.


util has a few functions to check if something is of a particular type (isArray, isDate, isError).

var util = require('util'); 
console.log(util.isArray([])); // true 
console.log(util.isArray({ length: 0 })); // false 
//from w  w  w .  j a  va2  s.  c o  m
console.log(util.isDate(new Date())); // true 
console.log(util.isDate({})); // false 

console.log(util.isError(new Error('This is an error'))); // true 
console.log(util.isError({ message: 'I have a message' })); // false