JavaScript Modules: A Beginner’s Guide - Deepstash
JavaScript Modules: A Beginner’s Guide

JavaScript Modules: A Beginner’s Guide


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JavaScript Modules: A Beginner’s Guide

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What modules are

Good authors divide their books into chapters and sections; good programmers divide their programs into modules.

Like a book chapter, modules are just clusters of words (or code, as the case may be).


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There are a lot of benefits to using modules in favor of a sprawling, interdependent codebase. 

  • Maintainability: By definition, a module is self-contained. 
  • Namespacing: In JavaScript, variables outside the scope of a top-level function are global (meaning, everyone can access them). Because of this, it’s common to have “namespace pollution”, where completely unrelated code shares global variables.
  • Reusability: Let’s be honest here: we’ve all copied code we previously wrote into new projects at one point or another.


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The Module pattern is used to mimic the concept of classes so that we can store both public and private methods and variables inside a single object — similar to how classes are used in other programming languages like Java or Python. 

That allows us to create a public-facing API for the methods that we want to expose to the world, while still encapsulating private variables and methods in a closure scope.


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  • CommonJS is a volunteer working group that designs and implements JavaScript APIs for declaring modules. A CommonJS module is essentially a reusable piece of JavaScript that exports specific objects, making them available for other modules to require in their programs.
  • Unlike CommonJS, AMD takes a browser-first approach alongside asynchronous behavior to get the job done. (Note, there are a lot of people who strongly believe that dynamically loading files piecemeal as you start to run code isn’t favorable, which we’ll explore more when in the next section on module-building).


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For projects that require you to support both AMD and CommonJS features, there’s yet another format: Universal Module Definition (UMD).

UMD essentially creates a way to use either of the two, while also supporting the global variable definition. As a result, UMD modules are capable of working on both client and server.


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