Detect whether PDF.js extension is installed in Google Chrome, Chromium or Opera.

detect-pdfjs-chromium.js

/**
 * Detects whether the PDF.js Chromium extension is installed in the browser.
 * Example: isPDFJSExtensionInstalled(function(result) { alert('Is PDF.js installed? ' + result);});
 *
 * @param {function(boolean)} callback - Called when the detection completed.
 *
 * Author: Rob Wu <rob@robwu.nl> (https://robwu.nl)
 * Public domain - all rights waived.
 */
function isPDFJSExtensionInstalled(callback) {
    if (!window.chrome) {
        // Not a Chromium browser.
        setTimeout(callback, 0, false);
        return;
    }
    if (chrome.webstore) {
        // Chrome or Chromium
        _isPDFJSExtensionInstalled('oemmndcbldboiebfnladdacbdfmadadm', callback);
    } else {
        // Opera? First detect PDF.js from Opera's addon gallery.
        // If not available, try to detect PDF.js from the Chrome Web Store
        _isPDFJSExtensionInstalled('encfpfilknmenlmjemepncnlbbjlabkc', function(result) {
            if (result) callback(true);
            else _isPDFJSExtensionInstalled('oemmndcbldboiebfnladdacbdfmadadm', callback);
        });
    }
    function _isPDFJSExtensionInstalled(id, callback) {
        var x = new XMLHttpRequest();
        x.open('GET', 'chrome-extension://' + id + '/content/web/viewer.html');
        x.onload = function() { callback(true); };
        x.onerror = function() { callback(false); };
        x.send();
    }
}

it seems that chrome has stopped this way to detect.