'addEventListener' of undefined

[gundogduyakici]

I open the Task page then
Uncaught TypeError: Cannot read property 'addEventListener' of undefined error ?

Detail:

this.$el.on('drop', function (e) {
                    e.preventDefault();
                    e.stopPropagation();
                    var e = e.originalEvent;
                    if (e.dataTransfer && e.dataTransfer.files && e.dataTransfer.files.length) {
                        this.uploadFiles(e.dataTransfer.files);
                    }
                }.bind(this));

               [COLOR=#FF0000][U] this.$el.get(0).addEventListener('dragover', function (e) {[/U][/COLOR]
                    e.preventDefault();
                }.bind(this));
                this.$el.get(0).addEventListener('dragleave', function (e) {
                    e.preventDefault();
                }.bind(this));
            }