picturefill.js

/*! Picturefill - Responsive Images that work today.
 *  Author: Scott Jehl, Filament Group, 2012 ( new proposal implemented by Shawn Jansepar )
 *  License: MIT/GPLv2
 *  Spec: http://picture.responsiveimages.org/
 */
(function( w, doc, image ) {
    // Enable strict mode
    "use strict";

    // If picture is supported, well, that's awesome. Let's get outta here...
    if ( w.HTMLPictureElement ) {
        w.picturefill = function() { };
        return;
    }

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

    // local object for method references and testing exposure
    var pf = {};

    // namespace
    pf.ns = "picturefill";

    // srcset support test
    (function() {
        pf.srcsetSupported = "srcset" in image;
        pf.sizesSupported = "sizes" in image;
    })();

    // just a string trim workaround
    pf.trim = function( str ) {
        return str.trim ? str.trim() : str.replace( /^\s+|\s+$/g, "" );
    };

    // just a string endsWith workaround
    pf.endsWith = function( str, suffix ) {
        return str.endsWith ? str.endsWith( suffix ) : str.indexOf( suffix, str.length - suffix.length ) !== -1;
    };

    /**
     * Shortcut method for https://w3c.github.io/webappsec/specs/mixedcontent/#restricts-mixed-content ( for easy overriding in tests )
     */
    pf.restrictsMixedContent = function() {
        return w.location.protocol === "https:";
    };
    /**
     * Shortcut method for matchMedia ( for easy overriding in tests )
     */

    pf.matchesMedia = function( media ) {
        return w.matchMedia && w.matchMedia( media ).matches;
    };

    // Shortcut method for `devicePixelRatio` ( for easy overriding in tests )
    pf.getDpr = function() {
        return ( w.devicePixelRatio || 1 );
    };

    /**
     * Get width in css pixel value from a "length" value
     * http://dev.w3.org/csswg/css-values-3/#length-value
     */
    pf.getWidthFromLength = function( length ) {
        // If a length is specified and doesn’t contain a percentage, and it is greater than 0 or using `calc`, use it. Else, use the `100vw` default.
        length = length && length.indexOf( "%" ) > -1 === false && ( parseFloat( length ) > 0 || length.indexOf( "calc(" ) > -1 ) ? length : "100vw";

        /**
         * If length is specified in  `vw` units, use `%` instead since the div we’re measuring
         * is injected at the top of the document.
         *
         * TODO: maybe we should put this behind a feature test for `vw`?
         */
        length = length.replace( "vw", "%" );

        // Create a cached element for getting length value widths
        if ( !pf.lengthEl ) {
            pf.lengthEl = doc.createElement( "div" );

            // Positioning styles help prevent padding/margin/width on `html` or `body` from throwing calculations off.
            pf.lengthEl.style.cssText = "border:0;display:block;font-size:1em;left:0;margin:0;padding:0;position:absolute;visibility:hidden";
        }

        pf.lengthEl.style.width = length;

        doc.body.appendChild(pf.lengthEl);

        // Add a class, so that everyone knows where this element comes from
        pf.lengthEl.className = "helper-from-picturefill-js";

        if ( pf.lengthEl.offsetWidth <= 0 ) {
            // Something has gone wrong. `calc()` is in use and unsupported, most likely. Default to `100vw` (`100%`, for broader support.):
            pf.lengthEl.style.width = doc.documentElement.offsetWidth + "px";
        }

        var offsetWidth = pf.lengthEl.offsetWidth;

        doc.body.removeChild( pf.lengthEl );

        return offsetWidth;
    };

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

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

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

    // test webp support, only when the markup calls for it
    pf.types[ "image/webp" ] = function() {
        // based on Modernizr's lossless img-webp test
        // note: asynchronous
        var type = "image/webp";

        image.onerror = function() {
            pf.types[ type ] = false;
            picturefill();
        };
        image.onload = function() {
            pf.types[ type ] = image.width === 1;
            picturefill();
        };
        image.src = "data:image/webp;base64,UklGRh4AAABXRUJQVlA4TBEAAAAvAAAAAAfQ//73v/+BiOh/AAA=";
    };

    /**
     * Takes a source element and checks if its type attribute is present and if so, supported
     * Note: for type tests that require a async logic,
     * you can define them as a function that'll run only if that type needs to be tested. Just make the test function call picturefill again when it is complete.
     * see the async webp test above for example
     */
    pf.verifyTypeSupport = function( source ) {
        var type = source.getAttribute( "type" );
        // if type attribute exists, return test result, otherwise return true
        if ( type === null || type === "" ) {
            return true;
        } else {
            // if the type test is a function, run it and return "pending" status. The function will rerun picturefill on pending elements once finished.
            if ( typeof( pf.types[ type ] ) === "function" ) {
                pf.types[ type ]();
                return "pending";
            } else {
                return pf.types[ type ];
            }
        }
    };

    // Parses an individual `size` and returns the length, and optional media query
    pf.parseSize = function( sourceSizeStr ) {
        var match = /(\([^)]+\))?\s*(.+)/g.exec( sourceSizeStr );
        return {
            media: match && match[1],
            length: match && match[2]
        };
    };

    // Takes a string of sizes and returns the width in pixels as a number
    pf.findWidthFromSourceSize = function( sourceSizeListStr ) {
        // Split up source size list, ie ( max-width: 30em ) 100%, ( max-width: 50em ) 50%, 33%
        //                            or (min-width:30em) calc(30% - 15px)
        var sourceSizeList = pf.trim( sourceSizeListStr ).split( /\s*,\s*/ ),
            winningLength;

        for ( var i = 0, len = sourceSizeList.length; i < len; i++ ) {
            // Match <media-condition>? length, ie ( min-width: 50em ) 100%
            var sourceSize = sourceSizeList[ i ],
            // Split "( min-width: 50em ) 100%" into separate strings
                parsedSize = pf.parseSize( sourceSize ),
                length = parsedSize.length,
                media = parsedSize.media;

            if ( !length ) {
                continue;
            }
            if ( !media || pf.matchesMedia( media ) ) {
                // if there is no media query or it matches, choose this as our winning length
                // and end algorithm
                winningLength = length;
                break;
            }
        }

        // pass the length to a method that can properly determine length
        // in pixels based on these formats: http://dev.w3.org/csswg/css-values-3/#length-value
        return pf.getWidthFromLength( winningLength );
    };

    pf.parseSrcset = function( srcset ) {
        /**
         * A lot of this was pulled from Boris Smus’ parser for the now-defunct WHATWG `srcset`
         * https://github.com/borismus/srcset-polyfill/blob/master/js/srcset-info.js
         *
         * 1. Let input (`srcset`) be the value passed to this algorithm.
         * 2. Let position be a pointer into input, initially pointing at the start of the string.
         * 3. Let raw candidates be an initially empty ordered list of URLs with associated
         *    unparsed descriptors. The order of entries in the list is the order in which entries
         *    are added to the list.
         */
        var candidates = [];

        while ( srcset !== "" ) {
            srcset = srcset.replace( /^\s+/g, "" );

            // 5. Collect a sequence of characters that are not space characters, and let that be url.
            var pos = srcset.search(/\s/g),
                url, descriptor = null;

            if ( pos !== -1 ) {
                url = srcset.slice( 0, pos );

                var last = url.slice(-1);

                // 6. If url ends with a U+002C COMMA character (,), remove that character from url
                // and let descriptors be the empty string. Otherwise, follow these substeps
                // 6.1. If url is empty, then jump to the step labeled descriptor parser.

                if ( last === "," || url === "" ) {
                    url = url.replace( /,+$/, "" );
                    descriptor = "";
                }
                srcset = srcset.slice( pos + 1 );

                // 6.2. Collect a sequence of characters that are not U+002C COMMA characters (,), and
                // let that be descriptors.
                if ( descriptor === null ) {
                    var descpos = srcset.indexOf( "," );
                    if ( descpos !== -1 ) {
                        descriptor = srcset.slice( 0, descpos );
                        srcset = srcset.slice( descpos + 1 );
                    } else {
                        descriptor = srcset;
                        srcset = "";
                    }
                }
            } else {
                url = srcset;
                srcset = "";
            }

            // 7. Add url to raw candidates, associated with descriptors.
            if ( url || descriptor ) {
                candidates.push({
                    url: url,
                    descriptor: descriptor
                });
            }
        }
        return candidates;
    };

    pf.parseDescriptor = function( descriptor, sizesattr ) {
        // 11. Descriptor parser: Let candidates be an initially empty source set. The order of entries in the list
        // is the order in which entries are added to the list.
        var sizes = sizesattr || "100vw",
            sizeDescriptor = descriptor && descriptor.replace( /(^\s+|\s+$)/g, "" ),
            widthInCssPixels = pf.findWidthFromSourceSize( sizes ),
            resCandidate;

        if ( sizeDescriptor ) {
            var splitDescriptor = sizeDescriptor.split(" ");

            for (var i = splitDescriptor.length - 1; i >= 0; i--) {
                var curr = splitDescriptor[ i ],
                    lastchar = curr && curr.slice( curr.length - 1 );

                if ( ( lastchar === "h" || lastchar === "w" ) && !pf.sizesSupported ) {
                    resCandidate = parseFloat( ( parseInt( curr, 10 ) / widthInCssPixels ) );
                } else if ( lastchar === "x" ) {
                    var res = curr && parseFloat( curr, 10 );
                    resCandidate = res && !isNaN( res ) ? res : 1;
                }
            }
        }
        return resCandidate || 1;
    };

    /**
     * Takes a srcset in the form of url/
     * ex. "images/pic-medium.png 1x, images/pic-medium-2x.png 2x" or
     *     "images/pic-medium.png 400w, images/pic-medium-2x.png 800w" or
     *     "images/pic-small.png"
     * Get an array of image candidates in the form of
     *      {url: "/foo/bar.png", resolution: 1}
     * where resolution is http://dev.w3.org/csswg/css-values-3/#resolution-value
     * If sizes is specified, resolution is calculated
     */
    pf.getCandidatesFromSourceSet = function( srcset, sizes ) {
        var candidates = pf.parseSrcset( srcset ),
            formattedCandidates = [];

        for ( var i = 0, len = candidates.length; i < len; i++ ) {
            var candidate = candidates[ i ];

            formattedCandidates.push({
                url: candidate.url,
                resolution: pf.parseDescriptor( candidate.descriptor, sizes )
            });
        }
        return formattedCandidates;
    };

    /**
     * if it's an img element and it has a srcset property,
     * we need to remove the attribute so we can manipulate src
     * (the property's existence infers native srcset support, and a srcset-supporting browser will prioritize srcset's value over our winning picture candidate)
     * this moves srcset's value to memory for later use and removes the attr
     */
    pf.dodgeSrcset = function( img ) {
        if ( img.srcset ) {
            img[ pf.ns ].srcset = img.srcset;
            img.removeAttribute( "srcset" );
        }
    };

    // Accept a source or img element and process its srcset and sizes attrs
    pf.processSourceSet = function( el ) {
        var srcset = el.getAttribute( "srcset" ),
            sizes = el.getAttribute( "sizes" ),
            candidates = [];

        // if it's an img element, use the cached srcset property (defined or not)
        if ( el.nodeName.toUpperCase() === "IMG" && el[ pf.ns ] && el[ pf.ns ].srcset ) {
            srcset = el[ pf.ns ].srcset;
        }

        if ( srcset ) {
            candidates = pf.getCandidatesFromSourceSet( srcset, sizes );
        }
        return candidates;
    };

    pf.applyBestCandidate = function( candidates, picImg ) {
        var candidate,
            length,
            bestCandidate;

        candidates.sort( pf.ascendingSort );

        length = candidates.length;
        bestCandidate = candidates[ length - 1 ];

        for ( var i = 0; i < length; i++ ) {
            candidate = candidates[ i ];
            if ( candidate.resolution >= pf.getDpr() ) {
                bestCandidate = candidate;
                break;
            }
        }

        if ( bestCandidate && !pf.endsWith( picImg.src, bestCandidate.url ) ) {
            if ( pf.restrictsMixedContent() && bestCandidate.url.substr(0, "http:".length).toLowerCase() === "http:" ) {
                if ( typeof console !== undefined ) {
                    console.warn( "Blocked mixed content image " + bestCandidate.url );
                }
            } else {
                picImg.src = bestCandidate.url;
                // currentSrc attribute and property to match
                // http://picture.responsiveimages.org/#the-img-element
                picImg.currentSrc = picImg.src;

                var style = picImg.style || {},
                    WebkitBackfaceVisibility = "webkitBackfaceVisibility" in style,
                    currentZoom = style.zoom;

                if (WebkitBackfaceVisibility) { // See: https://github.com/scottjehl/picturefill/issues/332
                    style.zoom = ".999";

                    WebkitBackfaceVisibility = picImg.offsetWidth;

                    style.zoom = currentZoom;
                }
            }
        }
    };

    pf.ascendingSort = function( a, b ) {
        return a.resolution - b.resolution;
    };

    /**
     * In IE9, <source> elements get removed if they aren't children of
     * video elements. Thus, we conditionally wrap source elements
     * using <!--[if IE 9]><video style="display: none;"><![endif]-->
     * and must account for that here by moving those source elements
     * back into the picture element.
     */
    pf.removeVideoShim = function( picture ) {
        var videos = picture.getElementsByTagName( "video" );
        if ( videos.length ) {
            var video = videos[ 0 ],
                vsources = video.getElementsByTagName( "source" );
            while ( vsources.length ) {
                picture.insertBefore( vsources[ 0 ], video );
            }
            // Remove the video element once we're finished removing its children
            video.parentNode.removeChild( video );
        }
    };

    /**
     * Find all `img` elements, and add them to the candidate list if they have
     * a `picture` parent, a `sizes` attribute in basic `srcset` supporting browsers,
     * a `srcset` attribute at all, and they haven’t been evaluated already.
     */
    pf.getAllElements = function() {
        var elems = [],
            imgs = doc.getElementsByTagName( "img" );

        for ( var h = 0, len = imgs.length; h < len; h++ ) {
            var currImg = imgs[ h ];

            if ( currImg.parentNode.nodeName.toUpperCase() === "PICTURE" ||
                ( currImg.getAttribute( "srcset" ) !== null ) || currImg[ pf.ns ] && currImg[ pf.ns ].srcset !== null ) {
                elems.push( currImg );
            }
        }
        return elems;
    };

    pf.getMatch = function( img, picture ) {
        var sources = picture.childNodes,
            match;

        // Go through each child, and if they have media queries, evaluate them
        for ( var j = 0, slen = sources.length; j < slen; j++ ) {
            var source = sources[ j ];

            // ignore non-element nodes
            if ( source.nodeType !== 1 ) {
                continue;
            }

            // Hitting the `img` element that started everything stops the search for `sources`.
            // If no previous `source` matches, the `img` itself is evaluated later.
            if ( source === img ) {
                return match;
            }

            // ignore non-`source` nodes
            if ( source.nodeName.toUpperCase() !== "SOURCE" ) {
                continue;
            }
            // if it's a source element that has the `src` property set, throw a warning in the console
            if ( source.getAttribute( "src" ) !== null && typeof console !== undefined ) {
                console.warn("The `src` attribute is invalid on `picture` `source` element; instead, use `srcset`.");
            }

            var media = source.getAttribute( "media" );

            // if source does not have a srcset attribute, skip
            if ( !source.getAttribute( "srcset" ) ) {
                continue;
            }

            // if there's no media specified, OR w.matchMedia is supported
            if ( ( !media || pf.matchesMedia( media ) ) ) {
                var typeSupported = pf.verifyTypeSupport( source );

                if ( typeSupported === true ) {
                    match = source;
                    break;
                } else if ( typeSupported === "pending" ) {
                    return false;
                }
            }
        }

        return match;
    };

    function picturefill( opt ) {
        var elements,
            element,
            parent,
            firstMatch,
            candidates,
            options = opt || {};

        elements = options.elements || pf.getAllElements();

        // Loop through all elements
        for ( var i = 0, plen = elements.length; i < plen; i++ ) {
            element = elements[ i ];
            parent = element.parentNode;
            firstMatch = undefined;
            candidates = undefined;

            // immediately skip non-`img` nodes
            if ( element.nodeName.toUpperCase() !== "IMG" ) {
                continue;
            }

            // expando for caching data on the img
            if ( !element[ pf.ns ] ) {
                element[ pf.ns ] = {};
            }

            // if the element has already been evaluated, skip it unless
            // `options.reevaluate` is set to true ( this, for example,
            // is set to true when running `picturefill` on `resize` ).
            if ( !options.reevaluate && element[ pf.ns ].evaluated ) {
                continue;
            }

            // if `img` is in a `picture` element
            if ( parent.nodeName.toUpperCase() === "PICTURE" ) {

                // IE9 video workaround
                pf.removeVideoShim( parent );

                // return the first match which might undefined
                // returns false if there is a pending source
                // TODO the return type here is brutal, cleanup
                firstMatch = pf.getMatch( element, parent );

                // if any sources are pending in this picture due to async type test(s)
                // remove the evaluated attr and skip for now ( the pending test will
                // rerun picturefill on this element when complete)
                if ( firstMatch === false ) {
                    continue;
                }
            } else {
                firstMatch = undefined;
            }

            // Cache and remove `srcset` if present and we’re going to be doing `picture`/`srcset`/`sizes` polyfilling to it.
            if ( parent.nodeName.toUpperCase() === "PICTURE" ||
                ( element.srcset && !pf.srcsetSupported ) ||
                ( !pf.sizesSupported && ( element.srcset && element.srcset.indexOf("w") > -1 ) ) ) {
                pf.dodgeSrcset( element );
            }

            if ( firstMatch ) {
                candidates = pf.processSourceSet( firstMatch );
                pf.applyBestCandidate( candidates, element );
            } else {
                // No sources matched, so we’re down to processing the inner `img` as a source.
                candidates = pf.processSourceSet( element );

                if ( element.srcset === undefined || element[ pf.ns ].srcset ) {
                    // Either `srcset` is completely unsupported, or we need to polyfill `sizes` functionality.
                    pf.applyBestCandidate( candidates, element );
                } // Else, resolution-only `srcset` is supported natively.
            }

            // set evaluated to true to avoid unnecessary reparsing
            element[ pf.ns ].evaluated = true;
        }
    }

    /**
     * Sets up picture polyfill by polling the document and running
     * the polyfill every 250ms until the document is ready.
     * Also attaches picturefill on resize
     */
    function runPicturefill() {
        picturefill();
        var intervalId = setInterval( function() {
            // When the document has finished loading, stop checking for new images
            // https://github.com/ded/domready/blob/master/ready.js#L15
            picturefill();
            if ( /^loaded|^i|^c/.test( doc.readyState ) ) {
                clearInterval( intervalId );
                return;
            }
        }, 250 );

        function checkResize() {
            var resizeThrottle;

            if ( !w._picturefillWorking ) {
                w._picturefillWorking = true;
                w.clearTimeout( resizeThrottle );
                resizeThrottle = w.setTimeout( function() {
                    picturefill({ reevaluate: true });
                    w._picturefillWorking = false;
                }, 60 );
            }
        }

        if ( w.addEventListener ) {
            w.addEventListener( "resize", checkResize, false );
        } else if ( w.attachEvent ) {
            w.attachEvent( "onresize", checkResize );
        }
    }

    runPicturefill();

    /* expose methods for testing */
    picturefill._ = pf;

    /* expose picturefill */
    if ( typeof module === "object" && typeof module.exports === "object" ) {
        // CommonJS, just export
        module.exports = picturefill;
    } else if ( typeof define === "function" && define.amd ) {
        // AMD support
        define( function() { return picturefill; } );
    } else if ( typeof w === "object" ) {
        // If no AMD and we are in the browser, attach to window
        w.picturefill = picturefill;
    }

} )( window, window.document, new window.Image() );