How to call a specific python function from within a Django template - javascript

I have a button to copy data from a user uploaded file to the clipboard in a specific format. I already have that data saved in the database as it was uploaded in a separate file form. I currently have it so that upon clicking the copy to clipboard button it is linked to a copy_data view in my views.py that requires an HTTP request which redirects to the current template containing the copy to clipboard button with something like this:
HttpResponseRedirect('previous/template/here')
This works fine except for the fact that since it links to my copy_data view which then redirects to the original view containing the button it reloads the entire page which is undesirable.
I think a better solution would be to somehow bind a python function directly to the button click rather than worrying about redirecting from one view to another.
I've found many examples using ajax, but haven't found any that work for my use case. I tried binding a click event to the button without any problems, but I am stuck on figuring out how to bind the python function with the click.
How can I bind a python function in my Django template upon a button press?

It's tough to tell for sure, but I think you're mixing synch/asynch paradigms here. When you generate requests with Ajax, you don't (generally) want to return a redirect, you want to return data. That might be JSON data or data formatted as a specific MIME type or even just text. One way this might look at a high level is:
def copy_data(request):
# get posted data
submitted = request.POST
# do whatever is necessary to create document
data = ???
# first, we'll need a response
resp = HttpResponse()
# set the content type, if needed
resp.content_type = 'text/???; charset=utf-8'
# response has a file-like interface
resp.write(data)
return resp
Obviously, this would need work to suit your purpose, but that's the high-level approach.
It doesn't sound like you're returning JSON, but there's a special response object for that now if you need it.

Related

how to commuincate between php and JS?

I am new to web development and I am trying to build my first website.
I am having some troubles because web development is dependant on several programming languages like PHP and JS, and the most difficult part for me is to communicate between these languages.
For example, I am trying to create a function that compresses a folder and generate a download link to that new archive, this can be easily done by PHP. However, when the user clicks the zip button, I also wish to display a pop-up window that tells the user to wait while the folder is being compressed, and when the compression is done I want to change the text on that pop-up and display the download link, and this, of course, requires JS.
I've tried many solutions but none of them seemed perfect for me, and I feel like that these solutions are quick and dirty, which I don't want.
If there is a secret I do not know, please tell me about so I can finally work with these languages as if they are a single language.
Also, if you can help me with my current problem, I would be extra grateful.
I just want to know how to construct a form that can call the JS function that displays the pop-up, then calls the PHP Zip_Folder function, and once the PHP function is done, I want to display the download link on the pop-up window.
This is my form code: (It only calls the javascript function that displays the pop-up)
<input type = 'button' onclick = 'Show_PopUP(\"Folder_to_zip\")' value = 'Download Folder'>
And this is the Show_PopUP function code:
function Show_PopUP(folder) {
var e = document.getElementById('Folder_Download_PopUp');
if(e.style.display == 'block')
e.style.display = 'none';
else {
e.style.display = 'block';}}
I already have the PHP function that compresses and generate a download link for the archive, so what I need now is a way to call it after the pop-up is displayed, and a way to print the download link on the pop-up once the function is done.
This might not be the best approach since I am a beginner, so if you have suggestions on how to get my task done without this complexity, I would be very happy.
Sorry if my question is too long, and thanks in advance for your help.
What you need to do is use these things called XHRs, or XMLHttpRequest (Google it), from within JavaScript to php, which basically is kind of like an invisible browser going to the php page behind the scenes and "loading" whatever the php page gives back, only this is all happening within JavaScript itself, so you can read that this "invisible page" loaded, which is from php, and do stuff with that, without actually refreshing the page. This process is known as AJAX (look it up)
What you can do is, when you set up this "invisible page", you can also send certain kinds of information along with it that the php page can read, and when it's done the php page can echo something back to the invisible page, which can then be read with JavaScript. This easy you can communicate between php and JavaScript, by sending certain values, in JavaScript, along with this invisible page, and waiting for php to echo something back to it, then reading that with JavaScript
So how do we actually do this?
First on the JavaScript side, we need to make this "invisible page", which is really not technically a page, it just does the sane thing as what is done to display any other web page, which is technically called a "request" since it's like asking the server for some data, it's basically "requesting" it, then when the server echoes something back, that's called he "response" to what was requested
So to make this new request in JavaScript we can do the following
var asking= new XMLHttpRequest ()
now that it as if an invisible page was created, but not yet navigated to anything, but we have to now metaphorically "enter in the URL" to this invisible page (without actually "navigating" to it yet) to do that we do
asking.open("GET", "pathToPHPpage.php?hi=there")
So the first part is called "GET" because we want to simply get a response back, without actually sending anything (if we were sending a file though, we would instead use "POST" then put the file date in the next step), then we enter in the URL to the php page that you want to get. If it's the same as the JavaScript page just put location.href instead, but it's important to add at least something to the end of the URL, notice the "?hi=there", you can call it anything, but it's important to have a question mark immediately following the .php page, then the name of something (in this case"hi") followed by it's value (in this case "there"), because the php page is able to read that, and give a different response back depending on what it says
Ok so now we have to actually "send" that request to the server, which is like metaphorically "navigating" to the URL on the invisible page, to do that
asking.send()
(And if you put "POST" before, you can add the date you want to send in between the parenthesis, usually in the form of a string but it can be different depending on the data, look it up for more reference)
Now, before we continue in the JS side, let's quickly switch over to PHP (doesn't have to be in this order though) to see what happened
We need to listen for any "requests" on the php page, that contain the name "hi" (since that's what we at the end of the URL before), to do that, around the top of PHP (technically anywhere in php though) we do
$isHi = $_GET["hi"];
if(isset ($isHi)) {
//Do some php code
echo "hi back!".$isHi;
}
Basically we just looked for the *hi" name in our "GET" request that was sent to PHP, we checked if it is "set", meaning not nulll, then we echoed some message back to JS, now let's listen for that message on the JavaScript side
Back to JS, after the .send line (or before), we need to listen for when the page echoes back.
To do that we check if it successfully loaded, because sometimes there can be errors, so let's do
asking.onreadstatechange= function () {
if(asking.readyState == 4 && asking.status==200) {
alert(asking.responseText)
} else alert("ooh something happened")
}
Now we have access to the response the php code gave us
You can extend this to other forms of communication, let me know if you have any questions

JavaScript: how to pass additional information to source page?

I have a website and when a user follows an internal link I would like to pass some extra information to a new page, so JavaScript on the destination page could do some useful highlighting.
There is an option to pass that information via the link parameters (GET), but it will generate lots of virtually duplicate pages and break pretty URLs concept. Another way is to make a webapp using AJAX, but it will also bound content to a single URL.
How can I transparently pass some information to the new page during navigation w/o messing with site's URL structure?
You could store the data in local storage or session storage, and retrieve it again on the destination page.
So you have a few options.
Form Submission
First option post a form with the data. Add a hidden form, on the anchor click capture the click event, set the hidden fields with the values you want to send to the next page, and submit the form. On the next page, read the post parameters in the backend and update the page.
Local Storage
On click of the anchor, set localStorage to the values you want to appear on the next page. When the next page loads, read the localStorage values and update the page. Note: The server will not have access to the values
Ajax with pushState
Use Ajax to submit the form. When the Ajax call returns, use window.history.pushState to update the url with whatever url you want to be displayed to the user.
One of the options not mentioned is to create a dirty URL:
/destination/param1/value1/...
then strip additional parameters at server-side and redirect:
/destination
keeping additional values stored at server-side (e.g. via sessions). I still prefer using sessionStorage in a real application, but it worth mentioning anyway.
What do you mean it will "bind content to a single url"? AJAX request is the first thing that comes to my mind as the solution to this problem. You dont have to use the url of the page to make the ajax request, you can build the url inside your javascript based on whatever conditions exist in your application.
Besides AJAX and passing parameters in the URL, the only other thing I can think of is to use Cookies. That of course runs into problems if the user has cookies disabled. I think an Ajax call to your server is the most robust way of handling the problem.

Retrieving data from browser to JavaScript

I have just started out working with JS and I've managed to post data from a MySQL db to the website using node.js, jade and plain JS.
Now I'm trying to do the other way around, i.e. getting data from the website, to the JS code and then inserting it into the db.
What I'm thinking is simply making a textfield with a button. When I fill the textfield and press the button it is collected by the JS script and the inserted to the DB.
I am however having problems with Jade and the listener and I'm unable to even do a console.log using the listener.
This is what I've got so far in my .jade file.
extends layout
script.
var something = function() {
console.log('something')
}
block content
button(onclick='something()') Click
The website renders nicely, but nothing is printed when I click the button.
If someone could give a hint on how to fetch the data in my .js file that would also be appreciated.
In the context of the WWW there are two places that JavaScript can run.
On the server, e.g. with node.js
On the browser, embedded in a <script> element
Since you want to put the data into a database on the server, you want to go with option 1. So don't use a <script> element.
Use a <form> (you could use client side JS to read the data from the form and send it to the server (Ajax) but that seems overcomplicated for your needs and should be layered on top of a plain HTML solution if you were to go down that route).
form(action="/myendpoint" method="post")
label
| Data
textarea(name="foo")
button Submit
Then you just need to write server side code to retrieve that. The specifics of that will depend on how you are implementing the HTTP server in Node.
The question How do you extract POST data in Node.js? provides some starting points.

Node.js form update with and without ajax

What would be the "best" approach to dealing with forms which have to work without and with JavaScript enabled?
Would it be better to create different routes for each, like
AJAX request: route "API/contact" and return res.send("message")
without JavaScript: route "contact"and return a redirect with a query param of "message"
Or in one route and detect xhr and render it depending on this?
Or is there a better way of dealing with the problem of taking the user to the res.send("") when the JavaScript isn't enabled to give the user feedback on the submit?
To clarify:
I have a site which is working with AJAX requests for its forms to avoid full page loads. It lacks the fallback when JavaScript is not enabled and thus when a user clicks submit on a form, he receives the data from the post back with res.send and it replaces the whole page, instead of the desired effect which would be to just update a label with the "success/fail" message. The question then remains as above which would be the neat way of dealing with this?
Probably the best thing to do would be to check the X-Requested-With header and check that it contains XMLHttpRequest (but this might get deprecated as the new fetch API will slowly come into browser.
Based on that value, you might want to return a JSON payload, or eventually trigger a server side rendering, therefore returning an HTML page ready-to-be-consumed.
As an alternative, you can return a redirect response with a particular query string value; once the page is loaded, you will check for that value (using qs for example, or deparam in jquery and manipulate the client side accordingly.
Your server routes have nothing to do with client-side javascript. You don't need javascript to receive a "res.send" message.

Can Django/Javascript handle conditional "Ajax" responses to HTTP POST requests?

How do I design a Django/Javascript application to provide for conditional Ajax responses to conventional HTTP requests?
On the server, I have a custom-built Form object. When the browser POSTS the form's data, the server checks the submitted data against existing data and rules (eg, if the form adds some entity to a database, does that entity already exist in the database?). If the data passes, the server saves, generates an ID number and adds it to the form's data, and passes the form and data back to the browser.
if request.method == 'POST':
formClass = form_code.getCustomForm()
thisForm = formClass(data=request.POST)
if thisForm.isvalid():
saveCheck = thisForm.saveData()
t = loader.get_template("CustomerForm.html")
c = Context({ 'expectedFormObj': thisForm })
(Note that my custom logic checking is in saveData() and is separate from the html validation done by isvalid().)
So far, standard Django (I hope). But if the data doesn't pass, I want to send a message to the browser. I suppose saveData() could put the message in an attribute of the form, and the template could check for that attribute, embed its data as javascript variable and include a javascript function to display the message. But passing all that form html back, just to add one message, seems inelegant (as does the standard Django form submission process, but never mind). In that case I'd like to just pass back the message.
Now I suppose I could tie a Javascript function to the html form's onsubmit event, and have that issue an XMLHttpRequest, and have the server respond to that based on the output of the saveData() call. But then the browser has two requests to the server outstanding (POST and XHR). Maybe a successful saveData() would rewrite the whole page and erase any potential for conflict. But I'd also have to get the server to sequence its response to the XHR to follow the response to the POST, and figure out how to communicate the saveData outcome to the response to the XHR. I suppose that is doable, even without the thread programming I don't know, but it seems messy.
I speculate that I might use javascript to make the browser's response conditional to something in the response to the POST request (either rewrite the whole page, or just display a message). But I suspect that the page's javascript hands control over the browser with the POST request, and that any response to the POST would just rewrite the page.
So can I design a process to pass back the whole form only if the server-side saveData() works, and a message that is displayed without rewriting the entire form if saveData() doesn't? If so, how?
Although you can arrange for your views to examine the request data to decide if the response should be an AJAXish or plain HTML, I don't really recommend it. Put AJAX request handlers in a separate URL structure, for instance all your regular html views have urls like /foo/bar and a corresponding api call for the same info would be /ajax/foo/bar.
Since most views will examine the request data, then do some processing, then create a python dictionary and pass that to the template engine, you can factor out the common parts to make this a little easier. the first few steps could be a generic sort of function that just returns the python dictionary, and then actual responses are composed by wrapping the handler functions in a template renderer or json encoder.
My usual workflow is to initially assume that the client has no javascript, (which is still a valid assumption; many mobile browsers have no JS) and implement the app as static GET and POST handlers. From there I start looking for the places where my app can benefit from a little client side scripting. For instance I'll usually redesign the forms to submit via AJAX type calls without reloading a page. These will not send their requests to the same URL/django view as the plain html form version would, since the response needs to be a simple success message in plain text or html fragment.
Similarly, getting data from the server is also redesigned to respond with a concise JSoN document to be processed into the page on the client. This also would be a separate URL/django view as the corresponding plain html for that resource.
When dealing with AJAX, I use this:
from django.utils import simplejson
...
status = simplejson.dumps({'status': "success"})
return HttpResponse(status, mimetype="application/json")
Then, AJAX (jQuery) can do what it wants based on the return value of 'status'.
I'm not sure exactly what you want with regards to forms. If you want an easier, and better form experience, I suggest checking out uni-form. Pinax has a good implementation of this in their voting app.
FYI, this isn't an answer...but it might help you think about it a different way
Here's the problem I'm running into...Google App Engine + jQuery Ajax = 405 Method Not Allowed.
So basically I get the thing to work using the outlined code, then I can't make the AJAX request :(.

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