Require is a statement that Node interprets as, in some sense, a getter function. For example, say you have a file named analysis.js, and the inside of your file looks like this,

function analyzeWeather(weather_data) {
  console.log('Weather information for ' + weather_data.time + ': ');
  console.log('Rainfall: ' + weather_data.precip);
  console.log('Temperature: ' + weather_data.temp);
  //More weather_data analysis/printing...
}

This file contains only the method, analyzeWeather(weather_data). If we want to use this function, it must be either used inside of this file, or copied to the file it wants to be used by. However, Node has included a very useful tool to help with code and file organization, which is modules.

In order to utilize our function, we must first export the function through a statement at the beginning. Our new file looks like this,

module.exports = {
  analyzeWeather: analyzeWeather
}
function analyzeWeather(weather_data) {
  console.log('Weather information for ' + weather_data.time + ': ');
  console.log('Rainfall: ' + weather_data.precip);
  console.log('Temperature: ' + weather_data.temp);
  //More weather_data analysis/printing...
}

With this small module.exports statement, our function is now ready for use outside of the file. All that is left to do is to use require().

When require'ing a function or file, the syntax is very similar. It is usually done at the beginning of the file and set to var's or const's for use throughout the file. For example, we have another file (on the same level as analyze.js named handleWeather.js that looks like this,

const analysis = require('./analysis.js');

weather_data = {
  time: '01/01/2001',
  precip: 0.75,
  temp: 78,
  //More weather data...
};
analysis.analyzeWeather(weather_data);

In this file, we are using require() to grab our analysis.js file. When used, we just call the variable or constant assigned to this require and use whatever function inside that is exported.

Node's require is also very helpful when used in tandem with an NPM package. Say, for example, you would like to use the NPM package require in a file named getWeather.js. After NPM installing your package through your command line (git install request), you are ready to use it. Your getWeather.js file might like look this,

var https = require('request');

//Construct your url variable...
https.get(url, function(error, response, body) {
  if (error) {
    console.log(error);
  } else {
    console.log('Response => ' + response);
    console.log('Body => ' + body);
  }
});

When this file is run, it first require's (imports) the package you just installed called request. Inside of the request file, there are many functions you now have access to, one of which is called get. In the next couple lines, the function is used in order to make an HTTP GET request.