How To Minify WordPress Scripts

What is Minification and Why Do I Need It?

Minification is the process in which scripts and styles are compressed (and sometimes combined) to reduce the filesize. Take, for example, the following library (carhartl/jquery-cookie):

/*!
 * jQuery Cookie Plugin v1.4.1
 * https://github.com/carhartl/jquery-cookie
 *
 * Copyright 2006, 2014 Klaus Hartl
 * Released under the MIT license
 */
(function (factory) {
	if (typeof define === 'function' && define.amd) {
		// AMD
		define(['jquery'], factory);
	} else if (typeof exports === 'object') {
		// CommonJS
		factory(require('jquery'));
	} else {
		// Browser globals
		factory(jQuery);
	}
}(function ($) {

	var pluses = /\+/g;

	function encode(s) {
		return config.raw ? s : encodeURIComponent(s);
	}

	function decode(s) {
		return config.raw ? s : decodeURIComponent(s);
	}

	function stringifyCookieValue(value) {
		return encode(config.json ? JSON.stringify(value) : String(value));
	}

	function parseCookieValue(s) {
		if (s.indexOf('"') === 0) {
			// This is a quoted cookie as according to RFC2068, unescape...
			s = s.slice(1, -1).replace(/\\"/g, '"').replace(/\\\\/g, '\\');
		}

		try {
			// Replace server-side written pluses with spaces.
			// If we can't decode the cookie, ignore it, it's unusable.
			// If we can't parse the cookie, ignore it, it's unusable.
			s = decodeURIComponent(s.replace(pluses, ' '));
			return config.json ? JSON.parse(s) : s;
		} catch(e) {}
	}

	function read(s, converter) {
		var value = config.raw ? s : parseCookieValue(s);
		return $.isFunction(converter) ? converter(value) : value;
	}

	var config = $.cookie = function (key, value, options) {

		// Write

		if (arguments.length > 1 && !$.isFunction(value)) {
			options = $.extend({}, config.defaults, options);

			if (typeof options.expires === 'number') {
				var days = options.expires, t = options.expires = new Date();
				t.setTime(+t + days * 864e+5);
			}

			return (document.cookie = [
				encode(key), '=', stringifyCookieValue(value),
				options.expires ? '; expires=' + options.expires.toUTCString() : '', // use expires attribute, max-age is not supported by IE
				options.path    ? '; path=' + options.path : '',
				options.domain  ? '; domain=' + options.domain : '',
				options.secure  ? '; secure' : ''
			].join(''));
		}

		// Read

		var result = key ? undefined : {};

		// To prevent the for loop in the first place assign an empty array
		// in case there are no cookies at all. Also prevents odd result when
		// calling $.cookie().
		var cookies = document.cookie ? document.cookie.split('; ') : [];

		for (var i = 0, l = cookies.length; i < l; i++) {
			var parts = cookies[i].split('=');
			var name = decode(parts.shift());
			var cookie = parts.join('=');

			if (key && key === name) {
				// If second argument (value) is a function it's a converter...
				result = read(cookie, value);
				break;
			}

			// Prevent storing a cookie that we couldn't decode.
			if (!key && (cookie = read(cookie)) !== undefined) {
				result[name] = cookie;
			}
		}

		return result;
	};

	config.defaults = {};

	$.removeCookie = function (key, options) {
		if ($.cookie(key) === undefined) {
			return false;
		}

		// Must not alter options, thus extending a fresh object...
		$.cookie(key, '', $.extend({}, options, { expires: -1 }));
		return !$.cookie(key);
	};

}));

That’s the full source for the jQuery Cookie plugin; it’s about 117 lines long and the filesize is approx 3.1 Kb. The current formatting is great if you’re going to be modifying the script, but chances are, you’re just using this script in production, so you don’t need it to be human readable.

The following is the same script, but minified.

/*! jquery.cookie v1.4.1 | MIT */
!function(a){"function"==typeof define&&define.amd?define(["jquery"],a):"object"==typeof exports?a(require("jquery")):a(jQuery)}(function(a){function b(a){return h.raw?a:encodeURIComponent(a)}function c(a){return h.raw?a:decodeURIComponent(a)}function d(a){return b(h.json?JSON.stringify(a):String(a))}function e(a){0===a.indexOf('"')&&(a=a.slice(1,-1).replace(/\\"/g,'"').replace(/\\\\/g,"\\"));try{return a=decodeURIComponent(a.replace(g," ")),h.json?JSON.parse(a):a}catch(b){}}function f(b,c){var d=h.raw?b:e(b);return a.isFunction(c)?c(d):d}var g=/\+/g,h=a.cookie=function(e,g,i){if(void 0!==g&&!a.isFunction(g)){if(i=a.extend({},h.defaults,i),"number"==typeof i.expires){var j=i.expires,k=i.expires=new Date;k.setTime(+k+864e5*j)}return document.cookie=[b(e),"=",d(g),i.expires?"; expires="+i.expires.toUTCString():"",i.path?"; path="+i.path:"",i.domain?"; domain="+i.domain:"",i.secure?"; secure":""].join("")}for(var l=e?void 0:{},m=document.cookie?document.cookie.split("; "):[],n=0,o=m.length;o>n;n++){var p=m[n].split("="),q=c(p.shift()),r=p.join("=");if(e&&e===q){l=f(r,g);break}e||void 0===(r=f(r))||(l[q]=r)}return l};h.defaults={},a.removeCookie=function(b,c){return void 0===a.cookie(b)?!1:(a.cookie(b,"",a.extend({},c,{expires:-1})),!a.cookie(b))}});

This has been reduced to 1.3 Kb, almost a 60% reduction in size, and this is a small script to start with! If you minify all your scripts and styles, you can vastly speed up your site’s load time, because it doesn’t need to load as much.

How Do I Minify Scripts in WordPress?

There’s an excellent plugin, written by OddOneOut, called Better WordPress Minify. After installing this plugin, go ahead and configure it. Here are some screen shots, although you probably will see the most improvement with the defaults:

Better WordPress Minify, Basic Settings Better WordPress Minify, Advanced Settings

Edit

This doesn’t play nice with symlinks; I was working on a website where I use SymLinks to version the site by linking to the chosen version of the files, and unfortunately, Better WordPress Minify doesn’t handle symlinks very well—It needs a symlink added to the symlinks array in its config file, min/config.php. It’s possible to add these and get it working, but I didn’t find it worth the hassle, as it requires a new entry every time you add a CSS/JS file. I will look into writing a fix for this.

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