plupload-runtimes.js

var Upload = {

    getDefaultRuntimes: function () {
        var runtimes = ['flash', 'html4'];
        var platform = navigator.platform || '';

        if (navigator.platform === 'Win32' && this.isSilverlightInstalled('4.0.0.0'))
            runtimes.unshift('silverlight');

        return runtimes.join(',');
    },

    isSilverlightInstalled: function (version) {
        // taken from plupload.silverlight.js
        var isVersionSupported = false, container = null, control = null, actualVer,
			actualVerArray, reqVerArray, requiredVersionPart, actualVersionPart, index = 0;

        try {
            try {
                control = new ActiveXObject('AgControl.AgControl');

                if (control.IsVersionSupported(version)) {
                    isVersionSupported = true;
                }

                control = null;
            } catch (e) {
                var plugin = navigator.plugins["Silverlight Plug-In"];

                if (plugin) {
                    actualVer = plugin.description;

                    if (actualVer === "1.0.30226.2") {
                        actualVer = "2.0.30226.2";
                    }

                    actualVerArray = actualVer.split(".");

                    while (actualVerArray.length > 3) {
                        actualVerArray.pop();
                    }

                    while (actualVerArray.length < 4) {
                        actualVerArray.push(0);
                    }

                    reqVerArray = version.split(".");

                    while (reqVerArray.length > 4) {
                        reqVerArray.pop();
                    }

                    do {
                        requiredVersionPart = parseInt(reqVerArray[index], 10);
                        actualVersionPart = parseInt(actualVerArray[index], 10);
                        index++;
                    } while (index < reqVerArray.length && requiredVersionPart === actualVersionPart);

                    if (requiredVersionPart <= actualVersionPart && !isNaN(requiredVersionPart)) {
                        isVersionSupported = true;
                    }
                }
            }
        } catch (e2) {
            isVersionSupported = false;
        }

        return isVersionSupported;
    }

};