# Minify [](https://pkg.go.dev/github.com/tdewolff/minify/v2?tab=doc) [](https://goreportcard.com/report/github.com/tdewolff/minify) [](https://codecov.io/gh/tdewolff/minify) [](https://www.patreon.com/tdewolff)
**[Online demo](https://go.tacodewolff.nl/minify)** if you need to minify files *now*.
**[Binaries](https://github.com/tdewolff/minify/releases) of CLI for various platforms.** See [CLI](https://github.com/tdewolff/minify/tree/master/cmd/minify) for more installation instructions.
**[Python bindings](https://pypi.org/project/tdewolff-minify/)** install with `pip install tdewolff-minify`
**[JavaScript bindings](https://www.npmjs.com/package/@tdewolff/minify)** install with `npm i @tdewolff/minify`
**[.NET bindings](https://github.com/JKamsker/NMinify)** install with `Install-Package NMinify` or `dotnet add package NMinify`, thanks to Jonas Kamsker for the port
---
*Did you know that the shortest valid piece of HTML5 is `x`? See for yourself at the [W3C Validator](http://validator.w3.org/)!*
Minify is a minifier package written in [Go][1]. It provides HTML5, CSS3, JS, JSON, SVG and XML minifiers and an interface to implement any other minifier. Minification is the process of removing bytes from a file (such as whitespace) without changing its output and therefore shrinking its size and speeding up transmission over the internet and possibly parsing. The implemented minifiers are designed for high performance (see https://github.com/privatenumber/minification-benchmarks where this library is (one of) the fastest JS minifiers).
The core functionality associates mimetypes with minification functions, allowing embedded resources (like CSS or JS within HTML files) to be minified as well. Users can add new implementations that are triggered based on a mimetype (or pattern), or redirect to an external command (like ClosureCompiler, UglifyCSS, ...).
### Sponsors
[](https://www.siteground.com/)
Please see https://www.patreon.com/tdewolff for ways to contribute, otherwise please contact me directly!
#### Table of Contents
- [Minify](#minify)
- [Prologue](#prologue)
- [Installation](#installation)
- [API stability](#api-stability)
- [Testing](#testing)
- [Performance](#performance)
- [HTML](#html)
- [Whitespace removal](#whitespace-removal)
- [CSS](#css)
- [JS](#js)
- [Comparison with other tools](#comparison-with-other-tools)
- [Compression ratio (lower is better)](#compression-ratio-lower-is-better)
- [Time (lower is better)](#time-lower-is-better)
- [JSON](#json)
- [SVG](#svg)
- [XML](#xml)
- [Usage](#usage)
- [New](#new)
- [From reader](#from-reader)
- [From bytes](#from-bytes)
- [From string](#from-string)
- [To reader](#to-reader)
- [To writer](#to-writer)
- [Middleware](#middleware)
- [Custom minifier](#custom-minifier)
- [Mediatypes](#mediatypes)
- [Examples](#examples)
- [Common minifiers](#common-minifiers)
- [External minifiers](#external-minifiers)
- [Closure Compiler](#closure-compiler)
- [UglifyJS](#uglifyjs)
- [esbuild](#esbuild)
- [Custom minifier](#custom-minifier-example)
- [ResponseWriter](#responsewriter)
- [Templates](#templates)
- [FAQ](#faq)
- [License](#license)
### Roadmap
- [ ] Use ASM/SSE to further speed-up core parts of the parsers/minifiers
- [x] Improve JS minifiers by shortening variables and proper semicolon omission
- [ ] Speed-up SVG minifier, it is very slow
- [x] Proper parser error reporting and line number + column information
- [ ] Generation of source maps (uncertain, might slow down parsers too much if it cannot run separately nicely)
- [ ] Create a cmd to pack webfiles (much like webpack), ie. merging CSS and JS files, inlining small external files, minification and gzipping. This would work on HTML files.
## Prologue
Minifiers or bindings to minifiers exist in almost all programming languages. Some implementations are merely using several regular expressions to trim whitespace and comments (even though regex for parsing HTML/XML is ill-advised, for a good read see [Regular Expressions: Now You Have Two Problems](http://blog.codinghorror.com/regular-expressions-now-you-have-two-problems/)). Some implementations are much more profound, such as the [YUI Compressor](http://yui.github.io/yuicompressor/) and [Google Closure Compiler](https://github.com/google/closure-compiler) for JS. As most existing implementations either use JavaScript, use regexes, and don't focus on performance, they are pretty slow.
This minifier proves to be that fast and extensive minifier that can handle HTML and any other filetype it may contain (CSS, JS, ...). It is usually orders of magnitude faster than existing minifiers.
## Installation
Make sure you have [Git](https://git-scm.com/) and [Go](https://golang.org/dl/) (1.18 or higher) installed, run
```
mkdir Project
cd Project
go mod init
go get -u github.com/tdewolff/minify/v2
```
Then add the following imports to be able to use the various minifiers
``` go
import (
"github.com/tdewolff/minify/v2"
"github.com/tdewolff/minify/v2/css"
"github.com/tdewolff/minify/v2/html"
"github.com/tdewolff/minify/v2/js"
"github.com/tdewolff/minify/v2/json"
"github.com/tdewolff/minify/v2/svg"
"github.com/tdewolff/minify/v2/xml"
)
```
You can optionally run `go mod tidy` to clean up the `go.mod` and `go.sum` files.
See [CLI tool](https://github.com/tdewolff/minify/tree/master/cmd/minify) for installation instructions of the binary.
### Docker
If you want to use Docker, please see https://hub.docker.com/r/tdewolff/minify.
```bash
$ docker run -it tdewolff/minify --help
```
## API stability
There is no guarantee for absolute stability, but I take issues and bugs seriously and don't take API changes lightly. The library will be maintained in a compatible way unless vital bugs prevent me from doing so. There has been one API change after v1 which added options support and I took the opportunity to push through some more API clean up as well. There are no plans whatsoever for future API changes.
## Testing
For all subpackages and the imported `parse` package, test coverage of 100% is pursued. Besides full coverage, the minifiers are [fuzz tested](https://github.com/tdewolff/fuzz) using [github.com/dvyukov/go-fuzz](http://www.github.com/dvyukov/go-fuzz), see [the wiki](https://github.com/tdewolff/minify/wiki) for the most important bugs found by fuzz testing. These tests ensure that everything works as intended and that the code does not crash (whatever the input). If you still encounter a bug, please file a [bug report](https://github.com/tdewolff/minify/issues)!
## Performance
The benchmarks directory contains a number of standardized samples used to compare performance between changes. To give an indication of the speed of this library, I've ran the tests on my Thinkpad T460 (i5-6300U quad-core 2.4GHz running Arch Linux) using Go 1.15.
```
name time/op
CSS/sample_bootstrap.css-4 2.70ms ± 0%
CSS/sample_gumby.css-4 3.57ms ± 0%
CSS/sample_fontawesome.css-4 767µs ± 0%
CSS/sample_normalize.css-4 85.5µs ± 0%
HTML/sample_amazon.html-4 15.2ms ± 0%
HTML/sample_bbc.html-4 3.90ms ± 0%
HTML/sample_blogpost.html-4 420µs ± 0%
HTML/sample_es6.html-4 15.6ms ± 0%
HTML/sample_stackoverflow.html-4 3.73ms ± 0%
HTML/sample_wikipedia.html-4 6.60ms ± 0%
JS/sample_ace.js-4 28.7ms ± 0%
JS/sample_dot.js-4 357µs ± 0%
JS/sample_jquery.js-4 10.0ms ± 0%
JS/sample_jqueryui.js-4 20.4ms ± 0%
JS/sample_moment.js-4 3.47ms ± 0%
JSON/sample_large.json-4 3.25ms ± 0%
JSON/sample_testsuite.json-4 1.74ms ± 0%
JSON/sample_twitter.json-4 24.2µs ± 0%
SVG/sample_arctic.svg-4 34.7ms ± 0%
SVG/sample_gopher.svg-4 307µs ± 0%
SVG/sample_usa.svg-4 57.4ms ± 0%
SVG/sample_car.svg-4 18.0ms ± 0%
SVG/sample_tiger.svg-4 5.61ms ± 0%
XML/sample_books.xml-4 54.7µs ± 0%
XML/sample_catalog.xml-4 33.0µs ± 0%
XML/sample_omg.xml-4 7.17ms ± 0%
name speed
CSS/sample_bootstrap.css-4 50.7MB/s ± 0%
CSS/sample_gumby.css-4 52.1MB/s ± 0%
CSS/sample_fontawesome.css-4 61.2MB/s ± 0%
CSS/sample_normalize.css-4 70.8MB/s ± 0%
HTML/sample_amazon.html-4 31.1MB/s ± 0%
HTML/sample_bbc.html-4 29.5MB/s ± 0%
HTML/sample_blogpost.html-4 49.8MB/s ± 0%
HTML/sample_es6.html-4 65.6MB/s ± 0%
HTML/sample_stackoverflow.html-4 55.0MB/s ± 0%
HTML/sample_wikipedia.html-4 67.5MB/s ± 0%
JS/sample_ace.js-4 22.4MB/s ± 0%
JS/sample_dot.js-4 14.5MB/s ± 0%
JS/sample_jquery.js-4 24.8MB/s ± 0%
JS/sample_jqueryui.js-4 23.0MB/s ± 0%
JS/sample_moment.js-4 28.6MB/s ± 0%
JSON/sample_large.json-4 234MB/s ± 0%
JSON/sample_testsuite.json-4 394MB/s ± 0%
JSON/sample_twitter.json-4 63.0MB/s ± 0%
SVG/sample_arctic.svg-4 42.4MB/s ± 0%
SVG/sample_gopher.svg-4 19.0MB/s ± 0%
SVG/sample_usa.svg-4 17.8MB/s ± 0%
SVG/sample_car.svg-4 29.3MB/s ± 0%
SVG/sample_tiger.svg-4 12.2MB/s ± 0%
XML/sample_books.xml-4 81.0MB/s ± 0%
XML/sample_catalog.xml-4 58.6MB/s ± 0%
XML/sample_omg.xml-4 159MB/s ± 0%
```
## HTML
HTML (with JS and CSS) minification typically shaves off about 10%.
The HTML5 minifier uses these minifications:
- strip unnecessary whitespace and otherwise collapse it to one space (or newline if it originally contained a newline)
- strip superfluous quotes, or uses single/double quotes whichever requires fewer escapes
- strip default attribute values and attribute boolean values
- strip some empty attributes
- strip unrequired tags (`html`, `head`, `body`, ...)
- strip unrequired end tags (`tr`, `td`, `li`, ... and often `p`)
- strip default protocols (`http:`, `https:` and `javascript:`)
- strip all comments (including conditional comments, old IE versions are not supported anymore by Microsoft)
- shorten `doctype` and `meta` charset
- lowercase tags, attributes and some values to enhance gzip compression
Options:
- `KeepSpecialComments` preserve all special comments, including Server Side Includes such as `` and IE conditional comments such as `` and ``, see https://msdn.microsoft.com/en-us/library/ms537512(v=vs.85).aspx#syntax
- `KeepDefaultAttrVals` preserve default attribute values such as `` // Faulty JS
req := httptest.NewRequest(http.MethodGet, "/", nil)
rec := httptest.NewRecorder()
m.Middleware(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
w.Header().Set("Content-Type", "text/html")
_, _ = w.Write([]byte(input))
if err = w.(io.Closer).Close(); err != nil {
panic(err)
}
})).ServeHTTP(rec, req)
}
```
#### ResponseWriter
``` go
func Serve(w http.ResponseWriter, r *http.Request) {
mw := m.ResponseWriter(w, r)
defer mw.Close()
w = mw
http.ServeFile(w, r, path.Join("www", r.URL.Path))
}
```
#### Custom response writer
ResponseWriter example which returns a ResponseWriter that minifies the content and then writes to the original ResponseWriter. Any write after applying this filter will be minified.
``` go
type MinifyResponseWriter struct {
http.ResponseWriter
io.WriteCloser
}
func (m MinifyResponseWriter) Write(b []byte) (int, error) {
return m.WriteCloser.Write(b)
}
// MinifyResponseWriter must be closed explicitly by calling site.
func MinifyFilter(mediatype string, res http.ResponseWriter) MinifyResponseWriter {
m := minify.New()
// add minfiers
mw := m.Writer(mediatype, res)
return MinifyResponseWriter{res, mw}
}
```
``` go
// Usage
func(w http.ResponseWriter, req *http.Request) {
w = MinifyFilter("text/html", w)
if _, err := io.WriteString(w, " This HTTP response will be minified.
"); err != nil {
panic(err)
}
if err := w.Close(); err != nil {
panic(err)
}
// Output: This HTTP response will be minified.
}
```
### Templates
Here's an example of a replacement for `template.ParseFiles` from `template/html`, which automatically minifies each template before parsing it.
Be aware that minifying templates will work in most cases but not all. Because the HTML minifier only works for valid HTML5, your template must be valid HTML5 of itself. Template tags are parsed as regular text by the minifier.
``` go
func compileTemplates(filenames ...string) (*template.Template, error) {
m := minify.New()
m.AddFunc("text/html", html.Minify)
var tmpl *template.Template
for _, filename := range filenames {
name := filepath.Base(filename)
if tmpl == nil {
tmpl = template.New(name)
} else {
tmpl = tmpl.New(name)
}
b, err := ioutil.ReadFile(filename)
if err != nil {
return nil, err
}
mb, err := m.Bytes("text/html", b)
if err != nil {
return nil, err
}
tmpl.Parse(string(mb))
}
return tmpl, nil
}
```
Example usage:
``` go
templates := template.Must(compileTemplates("view.html", "home.html"))
```
## FAQ
### Newlines remain in minified output
While you might expect the minified output to be on a single line for it to be fully minified, this is not true. In many cases, using a literal newline doesn't affect the file size, and in some cases it may even reduce the file size.
A typical example is HTML. Whitespace is significant in HTML, meaning that spaces and newlines between or around tags may affect how they are displayed. There is no distinction between a space or a newline and they may be interchanged without affecting the displayed HTML. Remember that a space (0x20) and a newline (0x0A) are both one byte long, so that there is no difference in file size when interchanging them. This minifier removes unnecessary whitespace by replacing stretches of spaces and newlines by a single whitespace character. Specifically, if the stretch of white space characters contains a newline, it will replace it by a newline and otherwise by a space. This doesn't affect the file size, but may help somewhat for debugging or file transmission objectives.
Another example is JavaScript. Single or double quoted string literals may not contain newline characters but instead need to escape them as `\n`. These are two bytes instead of a single newline byte. Using template literals it is allowed to have literal newline characters and we can use that fact to shave-off one byte! The result is that the minified output contains newlines instead of escaped newline characters, which makes the final file size smaller. Of course, changing from single or double quotes to template literals depends on other factors as well, and this minifier makes a calculation whether the template literal results in a shorter file size or not before converting a string literal.
## License
Released under the [MIT license](LICENSE.md).
[1]: http://golang.org/ "Go Language"