picturefill.js

/*! Picturefill - v3.0.2
 * http://scottjehl.github.io/picturefill
 * Copyright (c) 2015 https://github.com/scottjehl/picturefill/blob/master/Authors.txt;
 *  License: MIT
 */

(function( window, document, undefined ) {
	// Enable strict mode
	"use strict";

	// HTML shim|v it for old IE (IE9 will still need the HTML video tag workaround)
	document.createElement( "picture" );

	var warn, eminpx, alwaysCheckWDescriptor, evalId;
	// local object for method references and testing exposure
	var pf = {};
	var isSupportTestReady = false;
	var noop = function() {};
	var image = document.createElement( "img" );
	var getImgAttr = image.getAttribute;
	var setImgAttr = image.setAttribute;
	var removeImgAttr = image.removeAttribute;
	var docElem = document.documentElement;
	var types = {};
	var cfg = {
		//resource selection:
		algorithm: ""
	};
	var srcAttr = "data-pfsrc";
	var srcsetAttr = srcAttr + "set";
	// ua sniffing is done for undetectable img loading features,
	// to do some non crucial perf optimizations
	var ua = navigator.userAgent;
	var supportAbort = (/rident/).test(ua) || ((/ecko/).test(ua) && ua.match(/rv\:(\d+)/) && RegExp.$1 > 35 );
	var curSrcProp = "currentSrc";
	var regWDesc = /\s+\+?\d+(e\d+)?w/;
	var regSize = /(\([^)]+\))?\s*(.+)/;
	var setOptions = window.picturefillCFG;
	/**
	 * Shortcut property for https://w3c.github.io/webappsec/specs/mixedcontent/#restricts-mixed-content ( for easy overriding in tests )
	 */
	// baseStyle also used by getEmValue (i.e.: width: 1em is important)
	var baseStyle = "position:absolute;left:0;visibility:hidden;display:block;padding:0;border:none;font-size:1em;width:1em;overflow:hidden;clip:rect(0px, 0px, 0px, 0px)";
	var fsCss = "font-size:100%!important;";
	var isVwDirty = true;

	var cssCache = {};
	var sizeLengthCache = {};
	var DPR = window.devicePixelRatio;
	var units = {
		px: 1,
		"in": 96
	};
	var anchor = document.createElement( "a" );
	/**
	 * alreadyRun flag used for setOptions. is it true setOptions will reevaluate
	 * @type {boolean}
	 */
	var alreadyRun = false;

	// Reusable, non-"g" Regexes

	// (Don't use \s, to avoid matching non-breaking space.)
	var regexLeadingSpaces = /^[ \t\n\r\u000c]+/,
	    regexLeadingCommasOrSpaces = /^[, \t\n\r\u000c]+/,
	    regexLeadingNotSpaces = /^[^ \t\n\r\u000c]+/,
	    regexTrailingCommas = /[,]+$/,
	    regexNonNegativeInteger = /^\d+$/,

	    // ( Positive or negative or unsigned integers or decimals, without or without exponents.
	    // Must include at least one digit.
	    // According to spec tests any decimal point must be followed by a digit.
	    // No leading plus sign is allowed.)
	    // https://html.spec.whatwg.org/multipage/infrastructure.html#valid-floating-point-number
	    regexFloatingPoint = /^-?(?:[0-9]+|[0-9]*\.[0-9]+)(?:[eE][+-]?[0-9]+)?$/;

	var on = function(obj, evt, fn, capture) {
		if ( obj.addEventListener ) {
			obj.addEventListener(evt, fn, capture || false);
		} else if ( obj.attachEvent ) {
			obj.attachEvent( "on" + evt, fn);
		}
	};

	/**
	 * simple memoize function:
	 */

	var memoize = function(fn) {
		var cache = {};
		return function(input) {
			if ( !(input in cache) ) {
				cache[ input ] = fn(input);
			}
			return cache[ input ];
		};
	};

	// UTILITY FUNCTIONS

	// Manual is faster than RegEx
	// http://jsperf.com/whitespace-character/5
	function isSpace(c) {
		return (c === "\u0020" || // space
		        c === "\u0009" || // horizontal tab
		        c === "\u000A" || // new line
		        c === "\u000C" || // form feed
		        c === "\u000D");  // carriage return
	}

	/**
	 * gets a mediaquery and returns a boolean or gets a css length and returns a number
	 * @param css mediaqueries or css length
	 * @returns {boolean|number}
	 *
	 * based on: https://gist.github.com/jonathantneal/db4f77009b155f083738
	 */
	var evalCSS = (function() {

		var regLength = /^([\d\.]+)(em|vw|px)$/;
		var replace = function() {
			var args = arguments, index = 0, string = args[0];
			while (++index in args) {
				string = string.replace(args[index], args[++index]);
			}
			return string;
		};

		var buildStr = memoize(function(css) {

			return "return " + replace((css || "").toLowerCase(),
				// interpret `and`
				/\band\b/g, "&&",

				// interpret `,`
				/,/g, "||",

				// interpret `min-` as >=
				/min-([a-z-\s]+):/g, "e.$1>=",

				// interpret `max-` as <=
				/max-([a-z-\s]+):/g, "e.$1<=",

				//calc value
				/calc([^)]+)/g, "($1)",

				// interpret css values
				/(\d+[\.]*[\d]*)([a-z]+)/g, "($1 * e.$2)",
				//make eval less evil
				/^(?!(e.[a-z]|[0-9\.&=|><\+\-\*\(\)\/])).*/ig, ""
			) + ";";
		});

		return function(css, length) {
			var parsedLength;
			if (!(css in cssCache)) {
				cssCache[css] = false;
				if (length && (parsedLength = css.match( regLength ))) {
					cssCache[css] = parsedLength[ 1 ] * units[parsedLength[ 2 ]];
				} else {
					/*jshint evil:true */
					try{
						cssCache[css] = new Function("e", buildStr(css))(units);
					} catch(e) {}
					/*jshint evil:false */
				}
			}
			return cssCache[css];
		};
	})();

	var setResolution = function( candidate, sizesattr ) {
		if ( candidate.w ) { // h = means height: || descriptor.type === 'h' do not handle yet...
			candidate.cWidth = pf.calcListLength( sizesattr || "100vw" );
			candidate.res = candidate.w / candidate.cWidth ;
		} else {
			candidate.res = candidate.d;
		}
		return candidate;
	};

	/**
	 *
	 * @param opt
	 */
	var picturefill = function( opt ) {

		if (!isSupportTestReady) {return;}

		var elements, i, plen;

		var options = opt || {};

		if ( options.elements && options.elements.nodeType === 1 ) {
			if ( options.elements.nodeName.toUpperCase() === "IMG" ) {
				options.elements =  [ options.elements ];
			} else {
				options.context = options.elements;
				options.elements =  null;
			}
		}

		elements = options.elements || pf.qsa( (options.context || document), ( options.reevaluate || options.reselect ) ? pf.sel : pf.selShort );

		if ( (plen = elements.length) ) {

			pf.setupRun( options );
			alreadyRun = true;

			// Loop through all elements
			for ( i = 0; i < plen; i++ ) {
				pf.fillImg(elements[ i ], options);
			}

			pf.teardownRun( options );
		}
	};

	/**
	 * outputs a warning for the developer
	 * @param {message}
	 * @type {Function}
	 */
	warn = ( window.console && console.warn ) ?
		function( message ) {
			console.warn( message );
		} :
		noop
	;

	if ( !(curSrcProp in image) ) {
		curSrcProp = "src";
	}

	// Add support for standard mime types.
	types[ "image/jpeg" ] = true;
	types[ "image/gif" ] = true;
	types[ "image/png" ] = true;

	function detectTypeSupport( type, typeUri ) {
		// based on Modernizr's lossless img-webp test
		// note: asynchronous
		var image = new window.Image();
		image.onerror = function() {
			types[ type ] = false;
			picturefill();
		};
		image.onload = function() {
			types[ type ] = image.width === 1;
			picturefill();
		};
		image.src = typeUri;
		return "pending";
	}

	// test svg support
	types[ "image/svg+xml" ] = document.implementation.hasFeature( "http://www.w3.org/TR/SVG11/feature#Image", "1.1" );

	/**
	 * updates the internal vW property with the current viewport width in px
	 */
	function updateMetrics() {

		isVwDirty = false;
		DPR = window.devicePixelRatio;
		cssCache = {};
		sizeLengthCache = {};

		pf.DPR = DPR || 1;

		units.width = Math.max(window.innerWidth || 0, docElem.clientWidth);
		units.height = Math.max(window.innerHeight || 0, docElem.clientHeight);

		units.vw = units.width / 100;
		units.vh = units.height / 100;

		evalId = [ units.height, units.width, DPR ].join("-");

		units.em = pf.getEmValue();
		units.rem = units.em;
	}

	function chooseLowRes( lowerValue, higherValue, dprValue, isCached ) {
		var bonusFactor, tooMuch, bonus, meanDensity;

		//experimental
		if (cfg.algorithm === "saveData" ){
			if ( lowerValue > 2.7 ) {
				meanDensity = dprValue + 1;
			} else {
				tooMuch = higherValue - dprValue;
				bonusFactor = Math.pow(lowerValue - 0.6, 1.5);

				bonus = tooMuch * bonusFactor;

				if (isCached) {
					bonus += 0.1 * bonusFactor;
				}

				meanDensity = lowerValue + bonus;
			}
		} else {
			meanDensity = (dprValue > 1) ?
				Math.sqrt(lowerValue * higherValue) :
				lowerValue;
		}

		return meanDensity > dprValue;
	}

	function applyBestCandidate( img ) {
		var srcSetCandidates;
		var matchingSet = pf.getSet( img );
		var evaluated = false;
		if ( matchingSet !== "pending" ) {
			evaluated = evalId;
			if ( matchingSet ) {
				srcSetCandidates = pf.setRes( matchingSet );
				pf.applySetCandidate( srcSetCandidates, img );
			}
		}
		img[ pf.ns ].evaled = evaluated;
	}

	function ascendingSort( a, b ) {
		return a.res - b.res;
	}

	function setSrcToCur( img, src, set ) {
		var candidate;
		if ( !set && src ) {
			set = img[ pf.ns ].sets;
			set = set && set[set.length - 1];
		}

		candidate = getCandidateForSrc(src, set);

		if ( candidate ) {
			src = pf.makeUrl(src);
			img[ pf.ns ].curSrc = src;
			img[ pf.ns ].curCan = candidate;

			if ( !candidate.res ) {
				setResolution( candidate, candidate.set.sizes );
			}
		}
		return candidate;
	}

	function getCandidateForSrc( src, set ) {
		var i, candidate, candidates;
		if ( src && set ) {
			candidates = pf.parseSet( set );
			src = pf.makeUrl(src);
			for ( i = 0; i < candidates.length; i++ ) {
				if ( src === pf.makeUrl(candidates[ i ].url) ) {
					candidate = candidates[ i ];
					break;
				}
			}
		}
		return candidate;
	}

	function getAllSourceElements( picture, candidates ) {
		var i, len, source, srcset;

		// SPEC mismatch intended for size and perf:
		// actually only source elements preceding the img should be used
		// also note: don't use qsa here, because IE8 sometimes doesn't like source as the key part in a selector
		var sources = picture.getElementsByTagName( "source" );

		for ( i = 0, len = sources.length; i < len; i++ ) {
			source = sources[ i ];
			source[ pf.ns ] = true;
			srcset = source.getAttribute( "srcset" );

			// if source does not have a srcset attribute, skip
			if ( srcset ) {
				candidates.push( {
					srcset: srcset,
					media: source.getAttribute( "media" ),
					type: source.getAttribute( "type" ),
					sizes: source.getAttribute( "sizes" )
				} );
			}
		}
	}

	/**
	 * Srcset Parser
	 * By Alex Bell |  MIT License
	 *
	 * @returns Array [{url: _, d: _, w: _, h:_, set:_(????)}, ...]
	 *
	 * Based super duper closely on the reference algorithm at:
	 * https://html.spec.whatwg.org/multipage/embedded-content.html#parse-a-srcset-attribute
	 */

	// 1. Let input be the value passed to this algorithm.
	// (TO-DO : Explain what "set" argument is here. Maybe choose a more
	// descriptive & more searchable name.  Since passing the "set" in really has
	// nothing to do with parsing proper, I would prefer this assignment eventually
	// go in an external fn.)
	function parseSrcset(input, set) {

		function collectCharacters(regEx) {
			var chars,
			    match = regEx.exec(input.substring(pos));
			if (match) {
				chars = match[ 0 ];
				pos += chars.length;
				return chars;
			}
		}

		var inputLength = input.length,
		    url,
		    descriptors,
		    currentDescriptor,
		    state,
		    c,

		    // 2. Let position be a pointer into input, initially pointing at the start
		    //    of the string.
		    pos = 0,

		    // 3. Let candidates be an initially empty source set.
		    candidates = [];

		/**
		* Adds descriptor properties to a candidate, pushes to the candidates array
		* @return undefined
		*/
		// (Declared outside of the while loop so that it's only created once.
		// (This fn is defined before it is used, in order to pass JSHINT.
		// Unfortunately this breaks the sequencing of the spec comments. :/ )
		function parseDescriptors() {

			// 9. Descriptor parser: Let error be no.
			var pError = false,

			// 10. Let width be absent.
			// 11. Let density be absent.
			// 12. Let future-compat-h be absent. (We're implementing it now as h)
			    w, d, h, i,
			    candidate = {},
			    desc, lastChar, value, intVal, floatVal;

			// 13. For each descriptor in descriptors, run the appropriate set of steps
			// from the following list:
			for (i = 0 ; i < descriptors.length; i++) {
				desc = descriptors[ i ];

				lastChar = desc[ desc.length - 1 ];
				value = desc.substring(0, desc.length - 1);
				intVal = parseInt(value, 10);
				floatVal = parseFloat(value);

				// If the descriptor consists of a valid non-negative integer followed by
				// a U+0077 LATIN SMALL LETTER W character
				if (regexNonNegativeInteger.test(value) && (lastChar === "w")) {

					// If width and density are not both absent, then let error be yes.
					if (w || d) {pError = true;}

					// Apply the rules for parsing non-negative integers to the descriptor.
					// If the result is zero, let error be yes.
					// Otherwise, let width be the result.
					if (intVal === 0) {pError = true;} else {w = intVal;}

				// If the descriptor consists of a valid floating-point number followed by
				// a U+0078 LATIN SMALL LETTER X character
				} else if (regexFloatingPoint.test(value) && (lastChar === "x")) {

					// If width, density and future-compat-h are not all absent, then let error
					// be yes.
					if (w || d || h) {pError = true;}

					// Apply the rules for parsing floating-point number values to the descriptor.
					// If the result is less than zero, let error be yes. Otherwise, let density
					// be the result.
					if (floatVal < 0) {pError = true;} else {d = floatVal;}

				// If the descriptor consists of a valid non-negative integer followed by
				// a U+0068 LATIN SMALL LETTER H character
				} else if (regexNonNegativeInteger.test(value) && (lastChar === "h")) {

					// If height and density are not both absent, then let error be yes.
					if (h || d) {pError = true;}

					// Apply the rules for parsing non-negative integers to the descriptor.
					// If the result is zero, let error be yes. Otherwise, let future-compat-h
					// be the result.
					if (intVal === 0) {pError = true;} else {h = intVal;}

				// Anything else, Let error be yes.
				} else {pError = true;}
			} // (close step 13 for loop)

			// 15. If error is still no, then append a new image source to candidates whose
			// URL is url, associated with a width width if not absent and a pixel
			// density density if not absent. Otherwise, there is a parse error.
			if (!pError) {
				candidate.url = url;

				if (w) { candidate.w = w;}
				if (d) { candidate.d = d;}
				if (h) { candidate.h = h;}
				if (!h && !d && !w) {candidate.d = 1;}
				if (candidate.d === 1) {set.has1x = true;}
				candidate.set = set;

				candidates.push(candidate);
			}
		} // (close parseDescriptors fn)

		/**
		* Tokenizes descriptor properties prior to parsing
		* Returns undefined.
		* (Again, this fn is defined before it is used, in order to pass JSHINT.
		* Unfortunately this breaks the logical sequencing of the spec comments. :/ )
		*/
		function tokenize() {

			// 8.1. Descriptor tokeniser: Skip whitespace
			collectCharacters(regexLeadingSpaces);

			// 8.2. Let current descriptor be the empty string.
			currentDescriptor = "";

			// 8.3. Let state be in descriptor.
			state = "in descriptor";

			while (true) {

				// 8.4. Let c be the character at position.
				c = input.charAt(pos);

				//  Do the following depending on the value of state.
				//  For the purpose of this step, "EOF" is a special character representing
				//  that position is past the end of input.

				// In descriptor
				if (state === "in descriptor") {
					// Do the following, depending on the value of c:

				  // Space character
				  // If current descriptor is not empty, append current descriptor to
				  // descriptors and let current descriptor be the empty string.
				  // Set state to after descriptor.
					if (isSpace(c)) {
						if (currentDescriptor) {
							descriptors.push(currentDescriptor);
							currentDescriptor = "";
							state = "after descriptor";
						}

					// U+002C COMMA (,)
					// Advance position to the next character in input. If current descriptor
					// is not empty, append current descriptor to descriptors. Jump to the step
					// labeled descriptor parser.
					} else if (c === ",") {
						pos += 1;
						if (currentDescriptor) {
							descriptors.push(currentDescriptor);
						}
						parseDescriptors();
						return;

					// U+0028 LEFT PARENTHESIS (()
					// Append c to current descriptor. Set state to in parens.
					} else if (c === "\u0028") {
						currentDescriptor = currentDescriptor + c;
						state = "in parens";

					// EOF
					// If current descriptor is not empty, append current descriptor to
					// descriptors. Jump to the step labeled descriptor parser.
					} else if (c === "") {
						if (currentDescriptor) {
							descriptors.push(currentDescriptor);
						}
						parseDescriptors();
						return;

					// Anything else
					// Append c to current descriptor.
					} else {
						currentDescriptor = currentDescriptor + c;
					}
				// (end "in descriptor"

				// In parens
				} else if (state === "in parens") {

					// U+0029 RIGHT PARENTHESIS ())
					// Append c to current descriptor. Set state to in descriptor.
					if (c === ")") {
						currentDescriptor = currentDescriptor + c;
						state = "in descriptor";

					// EOF
					// Append current descriptor to descriptors. Jump to the step labeled
					// descriptor parser.
					} else if (c === "") {
						descriptors.push(currentDescriptor);
						parseDescriptors();
						return;

					// Anything else
					// Append c to current descriptor.
					} else {
						currentDescriptor = currentDescriptor + c;
					}

				// After descriptor
				} else if (state === "after descriptor") {

					// Do the following, depending on the value of c:
					// Space character: Stay in this state.
					if (isSpace(c)) {

					// EOF: Jump to the step labeled descriptor parser.
					} else if (c === "") {
						parseDescriptors();
						return;

					// Anything else
					// Set state to in descriptor. Set position to the previous character in input.
					} else {
						state = "in descriptor";
						pos -= 1;

					}
				}

				// Advance position to the next character in input.
				pos += 1;

			// Repeat this step.
			} // (close while true loop)
		}

		// 4. Splitting loop: Collect a sequence of characters that are space
		//    characters or U+002C COMMA characters. If any U+002C COMMA characters
		//    were collected, that is a parse error.
		while (true) {
			collectCharacters(regexLeadingCommasOrSpaces);

			// 5. If position is past the end of input, return candidates and abort these steps.
			if (pos >= inputLength) {
				return candidates; // (we're done, this is the sole return path)
			}

			// 6. Collect a sequence of characters that are not space characters,
			//    and let that be url.
			url = collectCharacters(regexLeadingNotSpaces);

			// 7. Let descriptors be a new empty list.
			descriptors = [];

			// 8. If url ends with a U+002C COMMA character (,), follow these substeps:
			//		(1). Remove all trailing U+002C COMMA characters from url. If this removed
			//         more than one character, that is a parse error.
			if (url.slice(-1) === ",") {
				url = url.replace(regexTrailingCommas, "");
				// (Jump ahead to step 9 to skip tokenization and just push the candidate).
				parseDescriptors();

			//	Otherwise, follow these substeps:
			} else {
				tokenize();
			} // (close else of step 8)

		// 16. Return to the step labeled splitting loop.
		} // (Close of big while loop.)
	}

	/*
	 * Sizes Parser
	 *
	 * By Alex Bell |  MIT License
	 *
	 * Non-strict but accurate and lightweight JS Parser for the string value <img sizes="here">
	 *
	 * Reference algorithm at:
	 * https://html.spec.whatwg.org/multipage/embedded-content.html#parse-a-sizes-attribute
	 *
	 * Most comments are copied in directly from the spec
	 * (except for comments in parens).
	 *
	 * Grammar is:
	 * <source-size-list> = <source-size># [ , <source-size-value> ]? | <source-size-value>
	 * <source-size> = <media-condition> <source-size-value>
	 * <source-size-value> = <length>
	 * http://www.w3.org/html/wg/drafts/html/master/embedded-content.html#attr-img-sizes
	 *
	 * E.g. "(max-width: 30em) 100vw, (max-width: 50em) 70vw, 100vw"
	 * or "(min-width: 30em), calc(30vw - 15px)" or just "30vw"
	 *
	 * Returns the first valid <css-length> with a media condition that evaluates to true,
	 * or "100vw" if all valid media conditions evaluate to false.
	 *
	 */

	function parseSizes(strValue) {

		// (Percentage CSS lengths are not allowed in this case, to avoid confusion:
		// https://html.spec.whatwg.org/multipage/embedded-content.html#valid-source-size-list
		// CSS allows a single optional plus or minus sign:
		// http://www.w3.org/TR/CSS2/syndata.html#numbers
		// CSS is ASCII case-insensitive:
		// http://www.w3.org/TR/CSS2/syndata.html#characters )
		// Spec allows exponential notation for <number> type:
		// http://dev.w3.org/csswg/css-values/#numbers
		var regexCssLengthWithUnits = /^(?:[+-]?[0-9]+|[0-9]*\.[0-9]+)(?:[eE][+-]?[0-9]+)?(?:ch|cm|em|ex|in|mm|pc|pt|px|rem|vh|vmin|vmax|vw)$/i;

		// (This is a quick and lenient test. Because of optional unlimited-depth internal
		// grouping parens and strict spacing rules, this could get very complicated.)
		var regexCssCalc = /^calc\((?:[0-9a-z \.\+\-\*\/\(\)]+)\)$/i;

		var i;
		var unparsedSizesList;
		var unparsedSizesListLength;
		var unparsedSize;
		var lastComponentValue;
		var size;

		// UTILITY FUNCTIONS

		//  (Toy CSS parser. The goals here are:
		//  1) expansive test coverage without the weight of a full CSS parser.
		//  2) Avoiding regex wherever convenient.
		//  Quick tests: http://jsfiddle.net/gtntL4gr/3/
		//  Returns an array of arrays.)
		function parseComponentValues(str) {
			var chrctr;
			var component = "";
			var componentArray = [];
			var listArray = [];
			var parenDepth = 0;
			var pos = 0;
			var inComment = false;

			function pushComponent() {
				if (component) {
					componentArray.push(component);
					component = "";
				}
			}

			function pushComponentArray() {
				if (componentArray[0]) {
					listArray.push(componentArray);
					componentArray = [];
				}
			}

			// (Loop forwards from the beginning of the string.)
			while (true) {
				chrctr = str.charAt(pos);

				if (chrctr === "") { // ( End of string reached.)
					pushComponent();
					pushComponentArray();
					return listArray;
				} else if (inComment) {
					if ((chrctr === "*") && (str[pos + 1] === "/")) { // (At end of a comment.)
						inComment = false;
						pos += 2;
						pushComponent();
						continue;
					} else {
						pos += 1; // (Skip all characters inside comments.)
						continue;
					}
				} else if (isSpace(chrctr)) {
					// (If previous character in loop was also a space, or if
					// at the beginning of the string, do not add space char to
					// component.)
					if ( (str.charAt(pos - 1) && isSpace( str.charAt(pos - 1) ) ) || !component ) {
						pos += 1;
						continue;
					} else if (parenDepth === 0) {
						pushComponent();
						pos +=1;
						continue;
					} else {
						// (Replace any space character with a plain space for legibility.)
						chrctr = " ";
					}
				} else if (chrctr === "(") {
					parenDepth += 1;
				} else if (chrctr === ")") {
					parenDepth -= 1;
				} else if (chrctr === ",") {
					pushComponent();
					pushComponentArray();
					pos += 1;
					continue;
				} else if ( (chrctr === "/") && (str.charAt(pos + 1) === "*") ) {
					inComment = true;
					pos += 2;
					continue;
				}

				component = component + chrctr;
				pos += 1;
			}
		}

		function isValidNonNegativeSourceSizeValue(s) {
			if (regexCssLengthWithUnits.test(s) && (parseFloat(s) >= 0)) {return true;}
			if (regexCssCalc.test(s)) {return true;}
			// ( http://www.w3.org/TR/CSS2/syndata.html#numbers says:
			// "-0 is equivalent to 0 and is not a negative number." which means that
			// unitless zero and unitless negative zero must be accepted as special cases.)
			if ((s === "0") || (s === "-0") || (s === "+0")) {return true;}
			return false;
		}

		// When asked to parse a sizes attribute from an element, parse a
		// comma-separated list of component values from the value of the element's
		// sizes attribute (or the empty string, if the attribute is absent), and let
		// unparsed sizes list be the result.
		// http://dev.w3.org/csswg/css-syntax/#parse-comma-separated-list-of-component-values

		unparsedSizesList = parseComponentValues(strValue);
		unparsedSizesListLength = unparsedSizesList.length;

		// For each unparsed size in unparsed sizes list:
		for (i = 0; i < unparsedSizesListLength; i++) {
			unparsedSize = unparsedSizesList[i];

			// 1. Remove all consecutive <whitespace-token>s from the end of unparsed size.
			// ( parseComponentValues() already omits spaces outside of parens. )

			// If unparsed size is now empty, that is a parse error; continue to the next
			// iteration of this algorithm.
			// ( parseComponentValues() won't push an empty array. )

			// 2. If the last component value in unparsed size is a valid non-negative
			// <source-size-value>, let size be its value and remove the component value
			// from unparsed size. Any CSS function other than the calc() function is
			// invalid. Otherwise, there is a parse error; continue to the next iteration
			// of this algorithm.
			// http://dev.w3.org/csswg/css-syntax/#parse-component-value
			lastComponentValue = unparsedSize[unparsedSize.length - 1];

			if (isValidNonNegativeSourceSizeValue(lastComponentValue)) {
				size = lastComponentValue;
				unparsedSize.pop();
			} else {
				continue;
			}

			// 3. Remove all consecutive <whitespace-token>s from the end of unparsed
			// size. If unparsed size is now empty, return size and exit this algorithm.
			// If this was not the last item in unparsed sizes list, that is a parse error.
			if (unparsedSize.length === 0) {
				return size;
			}

			// 4. Parse the remaining component values in unparsed size as a
			// <media-condition>. If it does not parse correctly, or it does parse
			// correctly but the <media-condition> evaluates to false, continue to the
			// next iteration of this algorithm.
			// (Parsing all possible compound media conditions in JS is heavy, complicated,
			// and the payoff is unclear. Is there ever an situation where the
			// media condition parses incorrectly but still somehow evaluates to true?
			// Can we just rely on the browser/polyfill to do it?)
			unparsedSize = unparsedSize.join(" ");
			if (!(pf.matchesMedia( unparsedSize ) ) ) {
				continue;
			}

			// 5. Return size and exit this algorithm.
			return size;
		}

		// If the above algorithm exhausts unparsed sizes list without returning a
		// size value, return 100vw.
		return "100vw";
	}

	// namespace
	pf.ns = ("pf" + new Date().getTime()).substr(0, 9);

	// srcset support test
	pf.supSrcset = "srcset" in image;
	pf.supSizes = "sizes" in image;
	pf.supPicture = !!window.HTMLPictureElement;

	// UC browser does claim to support srcset and picture, but not sizes,
	// this extended test reveals the browser does support nothing
	if (pf.supSrcset && pf.supPicture && !pf.supSizes) {
		(function(image2) {
			image.srcset = "data:,a";
			image2.src = "data:,a";
			pf.supSrcset = image.complete === image2.complete;
			pf.supPicture = pf.supSrcset && pf.supPicture;
		})(document.createElement("img"));
	}

	// Safari9 has basic support for sizes, but does't expose the `sizes` idl attribute
	if (pf.supSrcset && !pf.supSizes) {

		(function() {
			var width2 = "data:image/gif;base64,R0lGODlhAgABAPAAAP///wAAACH5BAAAAAAALAAAAAACAAEAAAICBAoAOw==";
			var width1 = "data:image/gif;base64,R0lGODlhAQABAAAAACH5BAEKAAEALAAAAAABAAEAAAICTAEAOw==";
			var img = document.createElement("img");
			var test = function() {
				var width = img.width;

				if (width === 2) {
					pf.supSizes = true;
				}

				alwaysCheckWDescriptor = pf.supSrcset && !pf.supSizes;

				isSupportTestReady = true;
				// force async
				setTimeout(picturefill);
			};

			img.onload = test;
			img.onerror = test;
			img.setAttribute("sizes", "9px");

			img.srcset = width1 + " 1w," + width2 + " 9w";
			img.src = width1;
		})();

	} else {
		isSupportTestReady = true;
	}

	// using pf.qsa instead of dom traversing does scale much better,
	// especially on sites mixing responsive and non-responsive images
	pf.selShort = "picture>img,img[srcset]";
	pf.sel = pf.selShort;
	pf.cfg = cfg;

	/**
	 * Shortcut property for `devicePixelRatio` ( for easy overriding in tests )
	 */
	pf.DPR = (DPR  || 1 );
	pf.u = units;

	// container of supported mime types that one might need to qualify before using
	pf.types =  types;

	pf.setSize = noop;

	/**
	 * Gets a string and returns the absolute URL
	 * @param src
	 * @returns {String} absolute URL
	 */

	pf.makeUrl = memoize(function(src) {
		anchor.href = src;
		return anchor.href;
	});

	/**
	 * Gets a DOM element or document and a selctor and returns the found matches
	 * Can be extended with jQuery/Sizzle for IE7 support
	 * @param context
	 * @param sel
	 * @returns {NodeList|Array}
	 */
	pf.qsa = function(context, sel) {
		return ( "querySelector" in context ) ? context.querySelectorAll(sel) : [];
	};

	/**
	 * Shortcut method for matchMedia ( for easy overriding in tests )
	 * whether native or pf.mMQ is used will be decided lazy on first call
	 * @returns {boolean}
	 */
	pf.matchesMedia = function() {
		if ( window.matchMedia && (matchMedia( "(min-width: 0.1em)" ) || {}).matches ) {
			pf.matchesMedia = function( media ) {
				return !media || ( matchMedia( media ).matches );
			};
		} else {
			pf.matchesMedia = pf.mMQ;
		}

		return pf.matchesMedia.apply( this, arguments );
	};

	/**
	 * A simplified matchMedia implementation for IE8 and IE9
	 * handles only min-width/max-width with px or em values
	 * @param media
	 * @returns {boolean}
	 */