Minification (also minimisation or minimization) is the process of removing all unnecessary characters from the

source code In computing, source code, or simply code or source, is a plain text computer program written in a programming language. A programmer writes the human readable source code to control the behavior of a computer. Since a computer, at base, only ...

of interpreted programming languages or

markup language A markup language is a Encoding, text-encoding system which specifies the structure and formatting of a document and potentially the relationships among its parts. Markup can control the display of a document or enrich its content to facilitate au ...

s without changing its functionality. These unnecessary characters usually include whitespace characters, new line characters, comments, and sometimes block delimiters, which are used to add readability to the code but are not required for it to execute. Minification reduces the size of the source code, making its transmission over a network (e.g. the Internet) more efficient. In programmer culture, aiming at extremely minified source code is the purpose of recreational code golf competitions and a part of the

demoscene The demoscene () is an international computer art subculture focused on producing demos: self-contained, sometimes extremely small, computer programs that produce audiovisual presentations. The purpose of a demo is to show off computer programmi ...

. Minification can be distinguished from the more general concept of

data compression In information theory, data compression, source coding, or bit-rate reduction is the process of encoding information using fewer bits than the original representation. Any particular compression is either lossy or lossless. Lossless compressi ...

in that the minified source can be interpreted immediately without the need for a decompression step: the same interpreter can work with both the original as well as with the minified source. The goals of minification are not the same as the goals of

obfuscation Obfuscation is the obscuring of the intended meaning of communication by making the message difficult to understand, usually with confusing and ambiguous language. The obfuscation might be either unintentional or intentional (although intent ...

; the former is often intended to be reversed using a pretty-printer or unminifier. However, to achieve its goals, minification sometimes uses techniques also used by

; for example, shortening variable names and refactoring the

. When minification uses such techniques, the pretty-printer or unminifier can only fully reverse the minification process if it is supplied details of the transformations done by such techniques. If not supplied those details, the reversed

will contain different variable names and control flow, even though it will have the same functionality as the original

Example

For example, the

JavaScript JavaScript (), often abbreviated as JS, is a programming language and core technology of the World Wide Web, alongside HTML and CSS. Ninety-nine percent of websites use JavaScript on the client side for webpage behavior. Web browsers have ...

code // This is a comment that will be removed by the minifier var array = []; for (var i = 0; i < 20; i++) is equivalent to but longer than for(var a=[],i=0;i<20;a[i]=i++);

History

In 2001 Douglas Crockford introduced JSMin, which removed comments and whitespace from JavaScript code. It was followed by YUI Compressor in 2007. In 2009, Google opened up its Closure toolkit, including Closure Compiler which contained a source mapping feature together with a Firefox extension called Closure Inspector. In 2010, Mihai Bazon introduced UglifyJS, which was superseded by UglifyJS2 in 2012; the rewrite was to allow for source map support. From 2017, Alex Lam took over maintenance and development of UglifyJS2, replacing it with UglifyJS3 which unified the CLI with the API. In 2018, Terser has been forked from uglify-es and has gained momentum since; in 2020 it outstripped UglifyJS when measured in daily downloads.

Source mapping

A source map is a

file format A file format is a Computer standard, standard way that information is encoded for storage in a computer file. It specifies how bits are used to encode information in a digital storage medium. File formats may be either proprietary format, pr ...

that allows software tools for

to display different code to a user than the code actually executed by the computer. For example, to aid in

debugging In engineering, debugging is the process of finding the Root cause analysis, root cause, workarounds, and possible fixes for bug (engineering), bugs. For software, debugging tactics can involve interactive debugging, control flow analysis, Logf ...

of minified code, by "mapping" this code to the original unminified

instead. The original format was created by Joseph Schorr as part of the Closure Inspector minification project. Version 2 and 3 of the format reduced the size of the map files considerably.

Types

Tools

Visual Studio Code comes with minification support for several languages. It can readily browse the Visual Studio Marketplace to download and install additional minifiers. JavaScript optimizers can minify and generate source maps. In addition certain online tools can compress CSS files.

Web development

Components and libraries for

Web application A web application (or web app) is application software that is created with web technologies and runs via a web browser. Web applications emerged during the late 1990s and allowed for the server to dynamically build a response to the request, ...

s and websites have been developed to optimize file requests and reduce page load times by shrinking the size of various files. JavaScript and Cascading Style Sheets (CSS) resources may be minified, preserving their behavior while considerably reducing their file size. Libraries available online are capable of minification and optimization to varying degrees. Some libraries also merge multiple script files into a single file for client download. JavaScript source maps can make code readable and debuggable even after it has been combined and minified.

References

{{Reflist Source code JavaScript