File Download

DownloadFile.js

Ext.define( 'DownloadFile', {

    requires:['Ext.form.Panel'],

    downloadFile:function ( config ) {
        config = config || {};
        var url = config.url,
            method = config.method || 'POST',// Either GET or POST. Default is POST.
            params = config.params || {};

        // Create form panel. It contains a basic form that we need for the file download.
        var form = Ext.create( 'Ext.form.Panel', {
            standardSubmit:true,
            url:url,
            method:method
        } );

        // Call the submit to begin the file download.
        form.submit( {
            target:'_blank', // Avoids leaving the page.
            params:params
        } );

        // Clean-up the form after 100 milliseconds.
        // Once the submit is called, the browser does not care anymore with the form object.
        Ext.defer( function () {
            form.close();
        }, 100 );

    }

} );

Tu use this:
include in your class with mixin:

mixins:['DownloadFile'],

and then in your class you can use:

 this.downloadFile( {
        method:'GET',
        url:'url/to/file.pdf',
        params:{
            foo:bar
        }
    } );