The ultimate guide to Minify JavaScript

How to Minify JavaScript

Ashkar Gomez
11min read
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Does your website load slowly and Visitors are hitting the back button faster?

Bulky images and slow servers will not always be the reason. One Such possible cause is bloated JavaScript.

JavaScript offers enhanced functionality and interactivity to the website. But the unoptimized JavaScript bloats the website causing slow loading times.

The solution for this problem is JavaScript Minification.

It is an effective method to streamline the JavaScript, reduce the file sizes and improve the loading time of the website significantly.

So, Are you Ready to say “GoodBye” to the website lag and “Hello” to happy visitors?

In this article, let’s explore in detail the power of minifying JavaScript.

What is JavaScript Minification?

JavaScript Minification is the process of reducing the size of JavaScript files by eliminating white space and unnecessary characters without compromising their functionality.

This also includes removing line breaks, comments, simplifying variables and function names.

The main objective of Minification is to minimize the file sizes which leads to faster website loading times, downloads and enhances website performance.

In production environments, minified JavaScript files are commonly used to improve user experience and optimize website speed.

Why is Minifying JavaScript important in SEO?

JavaScript Minification is important to Search Engine Optimization (SEO) for number of reasons as follows:

  • Minified JavaScript files lead to faster page loading speed which is a key ranking factor for search engines.
  • Faster page load times offer a better user experience by reducing the bounce rates and increasing engagement.
  • By ensuring that the websites are mobile friendly and perform well across various devices, minified JavaScript improves search rankings.
  • Reduced JavaScript files helps the search engines bots to crawl faster and easier to understand the content of the website resulting in more effective indexing.
  • Less data needs to be transferred with reduced JavaScript files. This saves the bandwidth consumption which is crucial for those on mobile data plans.

Why not use minified code from the beginning?

For optimizing website performance and potentially improving SEO, using minified code from the beginning may seem like a logical choice, but here are a few reasons why this isn’t usually done:

  • By eliminating whitespace, comments and variable names, minified code compromises readability.
  • If minified code were used from the start, it would be necessary to minify the code every time a change is made, which would add complexity and possibly slow down the development process.
  • Git and other version control systems would become more complicated if minified code was used from the start, as human-readable code is preferred by these systems for optimal performance.
  • Debugging errors and issues that arise during development is difficult with minified code.
  • Third-party libraries and frameworks are used in a lot of web projects. Minified versions of these libraries would have to be used if minified code was used from the start, which could make integration and debugging more difficult.

Thus, developers usually work with human-readable code during development and then minify the code as part of the build process before deploying it to production.

This method finds a balance between performance optimization, maintainability, and development efficiency.

Methods for Minifying JavaScript

JavaScript can be minified using a variety of methods, all of which aim to reduce the file size without sacrificing the functionality.

The following are some commonly used Techniques:

Removal of Whitespace – Eliminating unnecessary white space such as tabs, line breaks, Spaces can significantly reduce the file size without compromising the functionality of the code.

Both manual optimization techniques and minification tools can be used to achieve this.

Removal of Comments – Reducing the comments in JavaScript code can further minimize the file size.

While comments are not necessary for code execution, they are commonly used for documentation.

Single and Multi line comments can be removed from the code using minification tools.

Reducing Variables and Function Names – The function names and variables are renamed to shorter and more compact names. This will in turn minimize the length of identifiers and hence reduce the size of the file.

Identifiers are automatically renamed by minification tools to shorter names, usually utilizing alphanumeric characters.

Shortening the Literal values – Literal Values like strings and numbers can be optimized to reduce redundancy and file size even more.

Minification tools can minimize the representation of numeric values by optimizing them or by substituting variables for repeated string literals.

Mangling – Mangling is the aggressive renaming of functions and variables to even shorter names, frequently utilizing just one character.

Although this method can significantly reduce the file size, care must be taken to prevent unintended consequences like name conflicts and scope issues.

Elimination of Dead Code – Runtime performance can be enhanced and file size can be minified by removing unused and inaccessible code from JavaScript files.

Code segments that are not executed at runtime can be found and removed using the code analysis of minification tools.

Generation of Source Maps – This is an optional feature of minification tools.

Minification tools can generate source maps which map the minified code back to its original unminified source code.

When debugging minified code, Source maps helps the developers to identify the original source of errors and exceptions.

Guidelines to Minify JavaScript

The following are some best practices for Minifying JavaScript:

  • Before Minification always keep a backup copy of the original JavaScript files. This makes sure there will always be a point of reference in case needed to revert changes and debug issues.
  • Make sure the minified code doesn’t introduce any errors and maintains its functionality by giving it a thorough test. Any problems that develop during the minification process can be identified and fixed with the use of automated testing tools, Manual testing and unit tests.
  • To efficiently track changes, integrate minification into the version control workflow. To easily roll back changes made to either the original or minified JavaScript file use version Control systems such as Git.
  • JavaScript files should only be minified for production environments. To maintain code readability and to make debugging easier avoid minifying code while it is being developed.
  • Keep track of JavaScript files load order on the web page. To ensure proper page rendering and functionality, minified JavaScript files should be loaded after essential HTML content and critical CSS.
  • As a part of the build pipeline, automate the minification process by using build tools like Webpack, Gulp or Grunt. These tools offer plugins and configurations for minification allowing to easily minify the JavaScript files while the build is underway.

Some Common Tools for Minifying JavaScript

The following are some commonly used tools for minifying JavaScript:


It is the most commonly used JavaScript Minifier that can significantly minimize the size of the JavaScript files by eliminating unnecessary whitespaces, comments and renaming variables to more compact names.

It can be used with command line and also as a part of build procedures in task runners like Grunt and Gulp as it supports ES6+ syntax.


  • Provides Good Compression ratios.
  • Enables Integration into the build procedures using various task runners and bundlers.


  • Some users find configuration options to be complicated.
  • UglifyJS development has slowed down and it may not get updates or new features as often as other tools.

2.Google Closure Compiler

Google Closure Compiler is an effective JavaScript Optimization tool that not only minifies code but also performs advanced optimizations such as dead code elimination, variables renaming and function inlining.

It is offered by Google and can be utilized as a build process or web service component as well as a command-line tool.


  • Offers advanced optimization like variable renaming, the removal of dead code resulting in reduced file sizes.
  • Provides an API for Programmatic Access.


  • Compared to other tools, configuration and usage are more complicated.
  • Set up and integrate into build processes requires additional effort.


Terser is a modern JavaScript minifier known for its quick processing speed and superior compression ratios.

It is an improved version of UglifyJS with enhanced optimizations and better support for ECMAScript 6+.

Terser is frequently utilized with build tools such as Rollup and Webpack.


  • Constantly updated and kept in good working order.
  • Compatible with most bundlers and build tools.


  • Fewer sophisticated optimization options than Closure Compiler.
  • Some users find terser’s configuration options less extensive than other tools.


A module bundler commonly used in modern JavaScript development workflows is called Webpack.

It is pre-configured to support the use of plugins like terser-webpack-plugin and uglifyjs-webpack-plugin for minifying JavaScript code.

These plugins can be configured to minify the JavaScript code during the build process.


  • Convenient for webpack users as it is integrated into the build process.
  • It is possible to set it up to operate in production mode, which will automatically enable minification and other optimizations.


  • Minification may not be as adaptable as tools that are used independently.
  • The configuration may seem complicated to users who are unfamiliar with webpack.

5.Grunt and Gulp Plugins

There are several plugins available for developers who use task runners such as Grunt or Gulp to minify JavaScript code.

Examples – grunt-contrib-uglify for Grunt & gulp-uglify for Gulp

JavaScript minification can be effortlessly incorporated into your build process with the help of these plugins.


  • Grant plugins automate tasks and improve efficiency.
  • Gulp plugins offer faster build times specifically for the larger projects.


  • If not maintained properly, the Grant plugin creates new vulnerabilities.
  • Though the API is quite simple, the Gulp plugin will be challenging for those who are unfamiliar with build tools and asynchronous programming ideas.


In conclusion, JavaScript minification is an essential web development technique that reduces the size of JavaScript files and improves website performance.

By eliminating unnecessary characters such as whitespace and comments, as well as renaming variables to shorter names, JavaScript minification drastically reduces file sizes, leading to faster download times and improved page load speeds for users.

Incorporating JavaScript minification into the development process can lead to notable performance improvements, which in turn improve user experience, boost conversion rates, and ultimately leads to the success of web applications in today’s competitive online landscape.


Frequently Asked Questions

Does the Code's Functionality be affected with Minifying JavaScript?

If done correctly, minifying JavaScript should not have any effect on the functionality of the code.

But in order to make sure the minified code performs as expected, it must be thoroughly tested.

If unexpected changes to the code logic and errors happen during the minification process, Issues could occur.

Is it possible to revert minified JavaScript back to its Original Format?

Although it is technically possible, it is not advised to attempt this as the process is challenging to revert minified JavaScript back to its original format.

Meaning Formatting and variable names are removed during minification which makes the code difficult to understand and maintain.

For reference, it is advisable to maintain a backup of the original unminified code.

What are the Drawbacks of JavaScript Minification?

Though minifying JavaScript offers performance benefits, there are also some possible drawbacks to take into account.

Minified code is less readable and more difficult to maintain, which can make debugging and teamwork more challenging.

Also, if certain minification techniques applied incorrectly, it will unintentionally change the behavior of the code and introduce errors.

Picture of Ashkar Gomez

Ashkar Gomez

Ashkar Gomez is the Founder of 7 Eagles (a Growth Marketing & SEO Company). Ashkar started his career as a Sales Rep in 2013 and later shifted his career to SEO in 2014. He is one of the leading SEO experts in the industry with 8+ years of experience. He has worked on 200+ projects across 20+ industries in the United States, Canada, the United Kingdom, UAE, Australia, South Africa, and India. Besides SEO and Digital Marketing, he is passionate about Data Analytics, Personal Financial Planning, and Content Writing.

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