Node.js module wrapper function

Arguments

The arguments in the wrapper function are as follows:-

Note that every file in Node.js will wrap every file that it executes. To make it clear try running the following code in a Node.js environment and observe the output.

Code:

/*
  function(export, module, _filename, _dirname) {
      console.log(arguments);
  }
*/

console.log(arguments);

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Node.js wraps the code inside the node.js module wrapper function. Observe the commented code to understand how it works.

Output:

$node main.js
{ '0': {},
 '1': 
 { [Function: require]
   resolve: [Function: resolve],
   main: 
     Module {
       id: '.',
       exports: {},
       parent: null,
       filename: '/home/cg/root/5394193/main.js',
       loaded: false,
       children: [],
       paths: [Object] },
   extensions: { '.js': [Function], '.json': [Function], '.node': [Function] },
   cache: { '/home/cg/root/5394193/main.js': [Object] } },
 '2': 
 Module {
   id: '.',
   exports: {},
   parent: null,
   filename: '/home/cg/root/5394193/main.js',
   loaded: false,
   children: [],
   paths: 
     [ '/home/cg/root/5394193/node_modules',
       '/home/cg/root/node_modules',
       '/home/cg/node_modules',
       '/home/node_modules',
       '/node_modules' ] },
 '3': '/home/cg/root/5394193/main.js',
 '4': '/home/cg/root/5394193' }

Modifying node.js module wrapper function

Consider two files

1. main.js

var Module = require("module");
 
(function (moduleWrapCopy) {
 Module.wrap = function (script) {
  script = "console.log('modified the module wrapper function');" + script;
 
   return moduleWrapCopy(script);
 };
})(Module.wrap);
 
require("./module.js");

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2. module.js

console.log("Hello Ninja!");

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Every time a module is required in the main.js file, we overwrite the module.wrap function to console.log(‘modified the module wrapper function’). It gives a message if the modification is successful or not.

The output will be:

$ node main.js
modified the module wrapper function
Hello Ninja!

Also see - Difference between argument and parameter and Difference Between Controller and Restcontroller

Frequently asked questions

1. What are the advantages of the node.js module wrapper function?

The advantages of the node.js module wrapper function are-

• It keeps top-level variables that are defined with var, const, or let are scoped to the module rather than the global object.
• It helps to provide some global-looking variables that are actually specific to the module like module, exports, __filename, and __dirname.

2. What are the arguments present in the node.js module wrapper function?

The arguments present in the node.js module wrapper functions are exports, require, module, __filename, and __dirname.

Key takeaways

Node.js is a multithreaded, object-oriented open-source platform. The code is executed in such a way that the first code is wrapped inside a function called Node.js module wrapper. These functions that are created during the execution of the code have various parameters.

If you loved reading this article about the Node.js module wrapper function, check out What is Node.js? Where, When & How To Use It? and Why every web developer should learn Node.js?.