How to use functions from another file in Node.js using module.exports

In Node.js, all variables, functions, classes are visible to each other only within the same file. We are able to call functions from any other file. To do this, we will use require and module.exports.

First, create 2 files with which we work, server.js and index.js.

In server.js we just include index.js

var another = require('./index.js');

And all functions we will write in our index.js file

Lets add to index.js object which will contain all of our functions

var methods = {};

And add some functions

var methods = {
	timestamp: function() {
		console.log('Current Time in Unix Timestamp: ' + Math.floor(Date.now() / 1000));
	},
	currentDate: function() {
		console.log('Current Date is: ' + new Date().toISOString().slice(0, 10));
	}
};

or

methods.timestamp = function() {
	console.log('Current Time in Unix Timestamp: ' + Math.floor(Date.now() / 1000))
};
methods.currentDate = function() {
	console.log('Current Date is: ' + new Date().toISOString().slice(0, 10))
};

In order that we can use these functions in other files (in our example is server.js), we need to add at the end of index.js following code

exports.data = methods;

module.exports is a Node.js specific feature, it does not work with regular JavaScript

If you type in your server.js file

console.log(another)

you will see a similar message in the console

/user> node server.js
{ data: { timestamp: [Function], currentDate: [Function] } }

Now let’s use this functions. In server.js file, write a code that call the functions which we created above

another.data.timestamp();
another.data.currentDate();

In your terminal you should see the following

Current Time in Unix Timestamp: 1465804362
Current Date is: 2016-06-13

Note:

Instead of exports.data = methods; can be used module.exports = methods;. In this case, to call the functions, you should use

another.timestamp();
another.currentDate();

instead of

another.data.timestamp();
another.data.currentDate();

Consider another example:

var level = function(num) {
	return num > 40 ? "It's over 40!" : num;
};
module.exports = level;

When you connect the module using the require, in fact it will be the function that will allow you to do the following

require('./index.js')(50);

What is a simplified recording the following code

var level = require('./index.js')
level(50);