https://checkpointsystems.com/wp-content/plugins/ewww-image-optimizer/includes/check-webp.js?ver=880

1var ewww_webp_supported = false;
2// webp detection adapted from https://developers.google.com/speed/webp/faq#how_can_i_detect_browser_support_using_javascript
3function check_webp_feature(feature, callback) {
4	callback = (typeof callback !== 'undefined') ? callback : function(){};
5	if (ewww_webp_supported) {
6                callback(ewww_webp_supported);
7		return;
8	}
9        var kTestImages = {
10                alpha: "UklGRkoAAABXRUJQVlA4WAoAAAAQAAAAAAAAAAAAQUxQSAwAAAARBxAR/Q9ERP8DAABWUDggGAAAABQBAJ0BKgEAAQAAAP4AAA3AAP7mtQAAAA==",
11        };
12        var img = new Image();
13        img.onload = function () {
14                ewww_webp_supported = (img.width > 0) && (img.height > 0);
15		if (callback) {
16                	callback(ewww_webp_supported);
17		}
18        };
19        img.onerror = function () {
20		if (callback) {
21                	callback(false);
22		}
23        };
24        img.src = "data:image/webp;base64," + kTestImages[feature];
25}
26check_webp_feature('alpha');