Require()

This documentation focuses on explaining the uses and of the require() statement that NodeJS (opens new window) includes in their language.

Require is an import of certain files or packages used with NodeJS's modules. It is used to improve code structure and uses. require() is used on files that are installed locally, with a direct route from the file that is require'ing.

Beginning require() use with a function and file

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 (opens new window).

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 (opens new window)'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.

Beginning require() use with an NPM package

Node's require is also very helpful when used in tandem with an NPM package (opens new window). Say, for example, you would like to use the NPM package require (opens new window) in a file named getWeather.js. After NPM installing (opens new window) 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 (opens new window).

Syntax

• module.exports = {testFunction: testFunction};
• var test_file = require('./testFile.js'); //Let us have a file named testFile
• test_file.testFunction(our_data); //Let testFile have function testFunction

Remarks

Using require() allows code to be structured in a way similar to Java's use of classes (opens new window) and public methods. If a function is .export'ed, it can be require'ed in another file to be used. If a file is not .export'ed, it cannot be used in another file.