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// Copyright 2015 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
/*
* Looks on the page to find the image that could be the most representative
* one.
*/
(function() {
// Extract the referrer policy from the page.
var referrerPolicy = 'default';
var metaTags = document.getElementsByTagName('meta');
for (var i = 0; i < metaTags.length; ++i) {
if (metaTags[i].name.toLowerCase() == 'referrer') {
referrerPolicy = metaTags[i].content.toLowerCase();
break;
}
}
// See what to use for JSON. Some pages use a library that overrides JSON.
var jsonEncoder = JSON.stringify;
if (!jsonEncoder)
jsonEncoder = JSON.encode;
// First look if there is an Open Graph Image property available.
var ogImage = document.querySelector('meta[property=\"og:image\"]');
if (ogImage) {
// Checks that the url in ogImage has a path that contains more than just a
// simple '/'.
var url = ogImage.content;
var location = document.createElement('a');
location.href = url;
if (location.pathname.length > 1) {
return jsonEncoder({
'imageUrl': url,
'referrerPolicy': referrerPolicy
});
}
}
// Iterates through the images on the page, find the largest one that doesn't
// look like a banner.
var maxPointSize = 0;
var maxImage = null;
var images = document.getElementsByTagName('img');
for (var i = 0; i < images.length; i++) {
var currentImage = images[i];
var aspectRatio = currentImage.width / currentImage.height;
if (aspectRatio >= 2.4 || aspectRatio <= 0.5)
continue; // Skip weirdly shaped images. Those are ads or headers.
var pointSize = currentImage.width * currentImage.height;
if (pointSize > maxPointSize) {
maxPointSize = pointSize;
maxImage = currentImage;
}
}
// Only keep images larger than 320*160.
if (maxPointSize <= 51200.0 || maxImage === null)
return '';
return jsonEncoder({
'imageUrl': maxImage.src,
'referrerPolicy': referrerPolicy
});
})();
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