Gets proprietary CSS prefix for current browser - reduced from StyleFix

just-prefix.js

/**
 * prefix method reduced from StyleFix 1.0.2
 * @author Lea Verou
 * MIT license
 */
var prefix = (function() {
	if (!window.getComputedStyle) return '';
	
	var prefixes = {},
		properties = [],
		shorthands = {},
		style = getComputedStyle(document.documentElement, null),
		dummy = document.createElement('div').style;
	
	// Why are we doing this instead of iterating over properties in a .style object? Cause Webkit won't iterate over those.
	var iterate = function(property) {
		if(property.charAt(0) === '-') {
			properties.push(property);
			
			var parts = property.split('-'),
				prefix = parts[1];
				
			// Count prefix uses
			prefixes[prefix] = ++prefixes[prefix] || 1;
			
			// This helps determining shorthands
			while(parts.length > 3) {
				parts.pop();
				
				var shorthand = parts.join('-');

				if(supported(shorthand) && properties.indexOf(shorthand) === -1) {
					properties.push(shorthand);
				}
			}
		}
	},
	supported = function(property) {
		return property.replace(/-([a-z])/g, function($0, $1) {
			return $1.toUpperCase();
		}).replace('-','') in dummy;
	}
	
	// Some browsers have numerical indices for the properties, some don't
	if(style.length > 0) {
		for(var i=0; i<style.length; i++) {
			iterate(style[i])
		}
	}
	else {
		for(var property in style) {
			iterate(
				property.replace(/[A-Z]/g, function($0) {
					return '-' + $0.toLowerCase();
				})
			);
		}
	}
	
	// Find most frequently used prefix
	var highest = {uses:0};
	for(var prefix in prefixes) {
		var uses = prefixes[prefix];

		if(highest.uses < uses) {
			highest = {prefix: prefix, uses: uses};
		}
	}
	
	return '-' + highest.prefix + '-';
})();