Mobile file upload support detection

mob.upload.test.js

(function(a){
    
    "use strict";
    
    /**
     * Mobile file upload support detection
     * @constructor
     */
    function FileSupport() {
        // Support usage of the class without using the new keyword
        if (!(this instanceof FileSupport)) {
            return new FileSupport();
        }
        this.input = window.document.createElement('input');
        this.input.type  = "file";
        this.input.display = "none";
        this.supported = true;
        this.errMessage = "Sorry your browser does not support uploading files.";
    }
    
    /**
     * Runs regex on the navigation useragent to check for supported browsers
     * @return {Boolean}
     */
    FileSupport.prototype.isSupported = function() {
        // Try to insert a file element into the page so we can check if the broweser
        // is disabling the input
        try {
            window.document.getElementsByTagName("body")[0].appendChild(this.input);
            if (this.input.disabled) {
                this.supported = false;
            } else {
                this.supported = true;
            }
        } 
        // Set not supported if failed to create the element
        catch(e) {
            this.supported = false;
        }
        // Remove the element
        finally {
            this.input.parentNode.removeChild(this.input);
        }
        return this.supported;
    };
    
    /**
     * Checks if the browser supports file uploads
     * @param {Function} callBack 
     * @returns {Function}
     */
    FileSupport.prototype.check = function(callBack) {
        if (this.isSupported()) {
            callBack(null);
        } else {
            callBack(new Error(this.errMessage));
        }
    };
    
    // Attatch our library to the window object
    if (!a.FileSupport) {
        a.FileSupport = FileSupport; 
    }    
    
})(window);