Extjs 4 (with a code for 3.4 below) downloading a file returned from a post request

Question

I have seen questions slightly related to this, but none that answer my problem. I have set up an Ext.Ajax.request as follows:

var paramsStringVar = 'param1=1&param2=two&param3=something&param4=etc';

Ext.Ajax.request({
  url: '/cgi-bin/url.pl',
  method:'POST',
  params:paramsStringVar,
  timeout:120000,
  success: function(response, opts){
    var objhtml = response.responseText; //content returned from server side
    console.log(objhtml);
  }

});

This request retrieves the appropriate content from the backend. One parameter is outputType, which can take values {html, excel, csv}. When returning html to display I am able to handle and display it correctly. Now on to the problem...

When I set the outputType parameter to csv or excel, I get back the appropriate content as csv or tsv(excel) as requested. BUT, I don't want the content, I want a prompt to download the file(csv or excel). How can I have the browser auto prompt the user to download the file instead of just retrieving the text content within extjs?

Version 4.07 so I can't use any 4.1 only features

Answer 1

There seems to be no bulletproof solution but there are several approaches I would try:

1) Use an iframe instead of real XHR to POST data to the server, e.g. <form action="/something" target="myiframe"> where myiframe is the name of your hidden iframe. That way your form would use the iframe (not your main window) to submit data to the configured URL. Your server should set response header as application/octet-stream (or some ither MIME type for binary data) so the browser triggers download. Otherwise (if html returned in your case) you can just retrieve iframe's body innerHTML and display it to the user in UI. While using an iframe (or a new window) instead of XHR doesn't sound like the best idea, this solution seems to be the most reliable so far (and with best browser support).

Here is a slightly modified example from Ext.form.Basic docs page:

Ext.create('Ext.form.Panel', {
    title: 'Basic Form',
    renderTo: Ext.getBody(),
    width: 350,

    // Any configuration items here will be automatically passed along to
    // the Ext.form.Basic instance when it gets created.

    // *THIS* makes the form use a standard submit mechanism, not XHR
/**/standardSubmit: true,

    // URL to submit to
    url: 'save-form.php',

    items: [{
        fieldLabel: 'Field',
        xtype: 'textfield',
        name: 'theField'
    }],

    buttons: [{
        text: 'Submit',
        handler: function() {
            // The getForm() method returns the Ext.form.Basic instance:
            var form = this.up('form').getForm();
            if (form.isValid()) {
                // Submit the Ajax request and handle the response
                form.submit({
                    success: function(form, action) {
                       Ext.Msg.alert('Success', action.result.msg);
                    },
                    failure: function(form, action) {
                        Ext.Msg.alert('Failed', action.result.msg);
                    },

                    // You can put the name of your iframe here instead of _blank
                    // this parameter makes its way to Ext.form.Basic.doAction() 
                    // and further leads to creation of StandardSubmit action instance
/**/                target: '_blank'                        
                });
            }
        }
    }]
});

There are two key parameters here (lines marked with /**/):

1. standardSubmit: true config that you pass to your form will make it do a standard submit instead of XHR.
2. Passing a target parameter to the form's submit action. This feature is not documented but you can see it being used in Ext.form.action.Submit source code (all options that you pass to Ext.form.Basic.submit() method end up as parameters of Ext.form.action.* instance.

In the example code I put target: '_blank' to demonstrate that it works right away (will create a new browser window). You can replace it with the name of your iframe later but I suggest that you first test how your form submits data to a regular new window and then develop logic that creates and processes an iframe. You will have to process the result inside iframe yourself, thought. It's not that difficult, see Ext.data.Connection.upload() implementation as an example of iframe processing.

ExtJS actually already uses the iframe technique for file uploads. See Ext.data.Connection and Ext.form.field.Field.isFileUpload() for an idea of how it can work.

2) Suggested here: Using HTML5/Javascript to generate and save a file.

If you don't want to go the iframe way, you can try generate data URI from response data and navigate to that URI triggering download:

content = "Hello world!";
uriContent = "data:application/octet-stream," + encodeURIComponent(content);
window.location.href = uriContent;

Again, mimetype is essential here. This worked for me, you should note, however, that browsers impose a size limit to data URIs (256Kb is a safe bet).

3) Another answer in the mentioned thread links to FileSaver.js library the implements the (abandoned?) w3 spec. Usage and demo here. It uses [BlobBuilder] to generate a blob of binary data that is further used to initialize downloads using one of several methods. While this solution seems to work, it uses deprecated APIs and may not be future-proof.

Answer 2

Below is my solution. This is how I have it currently working. The response generates a download/open prompt, based on a response type of text/csv. Note that no iFrame or reference to an iframe are needed. I spent a lot of time hung up on the need for an iFrame, which actually broke my solution. An iFrame is not needed to generate a download prompt. What is needed is a request(submittal) similar to this one, along with a backend generating the appropriate csv with text/csv response header.

var hiddenForm = Ext.create('Ext.form.Panel', {
  title:'hiddenForm',
  standardSubmit: true,
  url: /cgi-bin/url.pl
  timeout: 120000,
  height:0,
  width: 0,
  hidden:true,
  items:[
    {xtype:'hiddenField', name:'field1', value:'field1Value'},
    // additional fields
  ]
})

hiddenForm.getForm().submit()

The standardSubmit line is vital