EXTJS IFRAME and security

Question

I am still new to web development, is it safe to use an IFRAME to download a file, my site is HTTPS and the iframe SRC url is also HTTPS, both are in the same domain. I am reading a lot about security risks but still joining the dots together.

This is the code I am using.

var iFrame = Ext.create('Ext.Component', {
            renderTo: Ext.getBody(),
            cls: 'x-hidden',
            id: 'iFrameId',
                autoEl: {
                    tag: 'iframe',
                    src: https_url
                }, 
            listeners: {
                afterrender: function () {
                    Ext.defer(function(){
                        // destory iframe after 3 minutes
                        iFrame.destroy()
                        },180000);
                    }
            }
        });