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Download file via POST in one request with JavaScript

Sometimes when making an HTTP request to download a file (e.g. PDF, XLSX, etc.) from the own webserver, it is necessary to use the HTTP method POST, because it requires dynamic input data. I have been trying different ways to reduce that to one single HTTP request for best performance, but could not succeed.
As JavaScript with the XMLHttpRequest object (AJAX) can not "download" files, I guess it requires an HTML workaround. The only working solution I found for that case is generating a form element wrapping input elements containing the data. I could not find a way how to send boolean values via this, as AJAX is able to. That would mean: it is not suitable for a standardizable implementation.
My question is: How can I download a file via one POST request which can include boolean values (JavaScript)?
In case it is important: The backend system I use is Ruby on Rails

As #Pointy mentioned, boolean values are always translated to strings in HTTP communication. I was wrong about that in my question. That means, converting a JavaScript JSON string or a classic object to an HTML form (then submitting and deleting it) works!
Actually sending an AJAX request and then manually triggering a link click to the generated file has the advantage of being able to use a progressbar.

How to allow user to save reports from a REST API?

My application has to generate reports which should be available for download in XLS format. I have built a REST API using Django Rest Framework and there is an endpoint for report generation. It accepts POST requests with JSON body (report parameters, like from, to, etc., but there is also some data that represented with JSON objects) and returns JSON result. I successfully use it from Javascript, render the report as an HTML table and it works just fine.
My problem is that I need to allow users to save the report as an .xls file with a decent filename (like myawesomereport.04.12-10.12.xls. I tried JS data url approach, but as far as I understand, there is no way to set a filename if you go with that option (except setting a download attribute on an a tag, but its support is limited, so it's not the way to go). I thought that maybe I should open a new window with my API endpoint's url appropriately formed, so it outputs an XLS file, but the problem is that I do not understand if there is a way to send JSON with that request.
How should I approach this problem?

You can set the filename in the backend, by using the header Content-Disposition, so that in the frontend you can use a standard <a> tag.
In DRF, it would look like this:
response['Content-Disposition'] = 'attachment; filename={}'.format(
file_name
)

Reading contents of an iframe with wikipedia source? [duplicate]

I am trying to implement a simple request to Wikipedia's API using AJAX (XMLHttpRequest). If I type the url in the address bar of Firefox, I get a neat XML, no sweat there. Yet, calling the exact same url with:
// this is my XMLHttpRequest object
httpObjectMain.open("GET", "http://en.wikipedia.org/w/api.php?action=query&format=xml&prop=langlinks&lllimit=500&titles=kaas", true);
httpObjectMain.send(null);
returns an empty response. According to FireBug, I get a 200 OK response, but the content is just empty.
I suspect I might be missing something on the header of the GET http request.
Help! (and thanks!)

The Wikipedia API does support JSONP.
Your query string'll become something like this:
http://en.wikipedia.org/w/api.php?action=query&format=json&callback=test&prop=langlinks&lllimit=500&titles=kaas
But you'll have to build the jsonp handler (or you can use your favorite library to do it), switch to json output format from the xml you choose and create the callback function to parse the result and do the stuff you need on the page.

The browser will not allow you to send an XHR to another domain other than the one the page is on. This is for security purposes.
One way around this that I have seen is to setup a proxy on the domain the page is hosted on that will pass requests through to the actual api server. See http://ajaxpatterns.org/Cross-Domain_Proxy

Javascript (client-side): Database query and Data handling

I have built a web application that accepts a Member_ID # from the client (javascript). The Member_ID is stored as a var in my javascript… now I need to make queries with it…first query to get member information (name) and then join tables to gather information for health plans that the member is elligible under … and so on.
As far as I can remember the concept is… send a async request to the server and wait for a response, once the response is received, store it and then parse it to extract useful information.
The end goal is to use the 'useful' information to plot graphs using HTML5 Canvas.
I need some direction with how to make the query? because when I read this forum, it is recommended that client-side query is 'bad' for a plethora of reasons.
Since most of my stuff is happening in the client side... few things in C# asp.net...how do I proceed?
It is also important to note that the web application should be accessible via the internet. outside the local network.
Does it make sense to Call a Web Service from the Client Side Using the AJAX Extension Toolkit??

You must handle it server side. Think about the ajax request as a simple POST or GET in the format of ?member_id=123&time=321 pointed at your handler file.
In your handler file you can construct your query from the request variables, execute it, and give a response by printing to the screen in either JSON or XML format.
Take a look here:
http://api.jquery.com/jQuery.ajax/
http://api.jquery.com/jQuery.getJSON/

Simple HTML POST without any server scripting, can be done using JS

I want to pass some textbox value strictly using POST from one html page to another...
how can this be done without using any server side language like asp.net or php
can it be done using javascript??
thnx

You can't read POST data in any way on javascript so this is not doable.
Here you can find similar questions:
http://forums.devshed.com/javascript-development-115/read-post-data-in-javascript-1172.html
http://www.sitepoint.com/forums/showthread.php?454963-Getting-GET-or-POST-variables-using-JavaScript
This reading can also be interesting: http://en.wikipedia.org/wiki/POST_%28HTTP%29
This expecially suggests why this answer (wikipedia is the source):
GET
Requests a representation of the specified resource. Requests using GET should only retrieve data and should have no other effect.
(This is also true of some other HTTP methods.)[1] The W3C has
published guidance principles on this distinction, saying, "Web
application design should be informed by the above principles, but
also by the relevant limitations."[10] See safe methods below.
POST
Submits data to be processed (e.g., from an HTML form) to the identified resource. The data is included in the body of the request.
This may result in the creation of a new resource or the updates of
existing resources or both.
POST data is added to the request. When you do a GET request the data is added to the url, and that's why you can access it through javascript (and that's why it's not parsed and you have to do it manually). Instead, POST send data directly into the http requests, which is not seen in any way by the html page (which is just a part of what is sent through the http request).
That said, only server side language will receive the full HTTP request, and definitely you can' access it by javascript.
I'm sorry but that is the real answer