Pass Dynamic Javascript Variable to Django/Python - javascript

I have looked at a number of answers and other websites, but none answer my specific question. I have a webpage with "+" and "-" buttons, which should increment a variable called "pieFact". This variable must be updated dynamically without having to refresh the page. It should then be passed to my Django view each time the value is changed. This will be used to update the size of pie charts in a web map. I have the following:
<button type="button" id=bttnMinus onclick="pieFact=pieFact*0.9">-</button>
<button type="button" id=bttnPlus onclick="pieFact=pieFact*1.1">+</button></td>
<script type="text.javascript">
var pieFact=0;
</script>
How can I pass the value of "pieFact" to Django? Based on my limited knowledge, I think I may have to use AJAX post/get.

In order to keep from refreshing the page, yes, you will need AJAX. I usually don't like to suggest libraries too much in answers, however, in the interest of being easily cross-browser compatible, I would suggest the use of jQuery.
With jQuery it would be as simple as
Inside of your django template
<html>
...
<head>
<script>
var URL = "{% url 'my_view_that_updates_pieFact' %}";
</script>
</head>
...
Later on...
You'll need to either POST or GET the data to the server via AJAX. To be more RESTful, whenever I need to send data to the server I use POST. jQuery provides the $.post() convenience function to AJAX data to a url via POST. The three parameters are the URL, the data to send (as a JavaScript object; think python dictionaries if you're not too familiar with JavaScript), and a callback function once the server sends back a response.
<script>
function updatePieFact(){
var data = {'pieFact': pieFact};
$.post(URL, data, function(response){
if(response === 'success'){ alert('Yay!'); }
else{ alert('Error! :('); }
});
}
The .click() functions are basically the same thing as specifying onlick in the html attribute. Both click events update pieFact as you would expect and then call updatePieFact() to send the value of pieFact to the server.
$(document).ready(function(){
$('#bttnMinus').click(function(){
pieFact *= 0.9;
updatePieFact();
});
$('#bttnPlus').click(function(){
pieFact *= 1.1;
updatePieFact();
});
});
</script>
In views.py
Since I've used the $.post() function in the JavaScript, the request that Django is going to receive is going to have a method of "POST", so I check to make sure that the method is indeed POST (this means that if someone visits the URL for this view with something like a GET request, they won't update anything). Once I see that the request is, in fact, a POST, I check to see if the key 'pieFact' is in the dict request.POST.
Remember when I set the variable data in the javascript to {'pieFact': pieFact}? That javascript just becomes the request.POST python dictionary. So, if in the javascript I had instead used var data = {'hello': pieFact};, then I would be checking if 'hello' in request.POST instead. Once I see that pieFact is in the request.POST dictionary, I can get its value and then do something with it. If everything is successful, I return an HttpResponse with the string 'success'. This correlates with the check in javascript: if(response === 'success').
def my_view_that_updates_pieFact(request):
if request.method == 'POST':
if 'pieFact' in request.POST:
pieFact = request.POST['pieFact']
# doSomething with pieFact here...
return HttpResponse('success') # if everything is OK
# nothing went well
return HttpRepsonse('FAIL!!!!!')
Hopefully that will get you pointed in the right direction.

Related

Ajax call. Passing value to another php file

I have a problem and hope you can help.
Ii have a status.PHP file containing a js.
STATUS.PHP
<? ..stuff... ?>
<html>
<head>
<title>BCM Status Page</title>
<script src="jquery-3.3.1.min.js"></script>
<script src="updater.js"></script>
</head>
<body bgcolor="#305c57" onload='init();'>
As you can see in the html ihave included a JS, during "onload" i'm calling the init() function of the javascript called updater.js
Now in the UPDATER.JS
function init() {
setInterval(read, 2000)
}
function read() {
$.ajax({
type: 'POST',
url: 'readDB.php',
dataType: 'jsonp',
success: function (data) {
console.log(data);
var json_obj = $.parseJSON(data);
console.log(json_obj[0].gwnumber);
},
error: function () {
console.log("Error loading data");
}
});
}
I'm doing an ajax call to the readDB.php that is working as intended, infact i have the correct value in the json_obj.
My question is: how can i get the json_obj value and pass it to the status.PHP file that is the one who's including the JS too?
Hope you can help. TY
Ok, there is a lot to say in this argument, but i will be the briefiest possible.
first things first
php and Javascript are two different programming language with a completely different paradigm.
The first is a back-end focused programming language;
Javascript instead is more front-end focused, just for entirety i have to mention that JS is used also for the backend part with a special eviroment called Node.js
back to the problem, the things that you are trying to do is not impossible but is excactly as you asked, your're idea (if i got it) was to pass the data from the js to the php like a parameter in a function...
the thing is that the php is elaborate and renderizated before in the server and the javascript is executed in the client, in the client web page there is no more footprint the php. This process is described very well at this link: http://php.net/manual/en/intro-whatis.php
The possible solution is:
FRONT-END(js): make another ajax call(request) to the same page that you are displaying with all the data that you want to elaborate.
BACK-END(php): controll if this request has been made, then access the data with the global variables $_POST & $_GET (depending on the type of the request), then elaborate this data.
if I can I suggest you to make a check if the manipulation that you want to do on those data need to be done in the server-side and not by the js!
Consider the order of execution:
User visits status.php
Browser requests status.php
Server executes status.php and sends response to browser
JS requests readDB.php
Browser requests readDB.php
Server executes readDB.php and sends response to browser
JS processes response
Go To 4
By the time you get to 7, it is too late to influence what happens at step 2.
You could make a new Ajax request to status.php and process the response in JS, but since status.php returns an entire HTML document, that doesn't make sense.
You could use location to load a new page using a URL that includes status.php and a query string with information from the Ajax response, but that would making using Ajax in the first place pointless.
You should probably change readDB.php to return *all** the data you need, and then using DOM methods (or jQuery wrappers around them) to modify the page the user is already looking at.
The simpliest and fastest (maybe not the sexiest way) to do it :
create global variable var respondData; in STATUS.PHP
within you ajax request on success function assign your data callback to it
respondData = data;
Now you have an access to it from every place in your code even when the ajax request is done. Just bare in mind to ensure you will try to access this variable after the page will fully load and after ajax will process the request. Otherwise you will get 'undefined'

Django: reverse parametrized url in JavaScript

let's say one of my urlpatterns looks like this.
url('^objects/update/(?P<pk>\d+)$', views.UpdateView.as_view(), name = 'update-object'),
I need to redirect user to the update page depending on the selected object (the list of objects is populated using Ajax). So I'd like to pass that named url pattern to the JavaScript, in order to build the actual url on the client side.
Example of what I want to achieve:
pass the name 'update-objects' to the function
get the actual url pattern, replace (?P<pk>..) with {pk}
pass the result to the javascript, resulting in : objects/update/{pk}
any tips?
thanks
to make it more clear: at the moment of rendering, I can't do url reverse because the PK is not known yet. I need to make kind of javascript-urlpattern which will later be converted to the real url (i.e. my JS code will replace {pk} part with the actual pk value)
The actual URL reversing must happen on the server side. There are several ways to do this, and the most elegant of these probably depends on how exactly your script and markup are set up for this. One thing I've done recently is to attach the URL to a logical element using HTML5 data attributes, which are easy to retrieve using jQuery. If you're not using jQuery, I'll leave it up to you to translate to pure JS. You haven't provided any code or specifics for your client-side, so I'm kind of shooting in the dark here, but maybe this will give you the idea:
Django HTML template:
<ul class="object-list">
{% for object in objectList %}
<li data-update-url="{% url update-objects object.pk %}">object.name</li>
{% endfor %}
</ul>
JS:
$('.object-list').on('click', 'li' function () {
var updateUrl = $(this).data('update-url')
...
});
It sounds like you need to make an additional ajax call once the object has actually been selected. Don't try and second guess your url.conf by trying to work out the url on the client side - you'd just be making trouble for yourself later. Wait till you can get a pk, then use django's reverse function to give you your url (doing anything else violates DRY).
How about creating a simple view that returns the url -
from django.core.urlresolvers import reverse
from django.http import HttpResponse, HttpResponseBadRequest
def get_url(request):
if request.is_ajax() and request.method == 'POST':
obj_id = request.POST['obj_id']
url = reverse('object-update', kwargs{'pk': obj_id})
return HttpResponse(obj_id)
return HttpResponseBadRequest()
Then write a javascript function that gets the url using an ajax call to your new view and then redirects. You'd call this function as soon as the object's been selected. I would suggest using JQuery to do this, pure javascript will require you to write more code, and probably write browser specific code (depending on your target). Also it supports dealing with django's csrf protection (you'll need to implement this for ajax calls if you haven't already).
var redirect = function(obj) {
$.ajax({
url: '/your-get-url-view/',
method: 'post',
data: {'obj_id': obj},
success: function(url){
window.location = url;
}
});
}
I'm afraid I don't know how you're getting from the selected object to the pk (For simplicity I've assumed it's available to the redirect function) - you may have to do some processing in the view to get there.
I haven't tested the above code, but it should give you an idea of what I'm suggesting.
Try this one:
Reverse method for generating Django urls
https://github.com/mlouro/django-js-utils
One more
https://github.com/Dimitri-Gnidash/django-js-utils
If you have a URL that only has one PK field in it, you could resolve it with any number (e.g. 0), then substitute the number as required.
In my scenario my URL had a pk then an upload_id, so I had to replace on the right most instance of a 0, with <upload_id>, which the JS would replace this string occurance as required:
detele_url_upload_id_0 = reverse(f'{APP_NAME}:api_upload_delete', args=[pk, 0])
prefix, suffix = detele_url_upload_id_0.rsplit('0', 1)
context['generic_delete_url'] = prefix + '<upload_id>' + suffix
Then in the JS:
const deleteUrl = genericDeleteUrl.replace('<upload_id>', uploadId)

How can I use jQuery to run MySQL queries?

Is it possible to run a MySQL query using jQuery? I'm trying to emulate the functionality of voting on SE sites.
The vote counter on SE automatically updates without the need to reload the page (which is what I currently have, a hidden form that re-submits to the current page but runs a small block on PHP that updates the score of a question in the database). I'm assuming that is being done using Javascript/jQuery seeing as it is dynamic.
How can I do this? Is there a library which makes it easy and simple (like PHP)?
You can use ajax to call a server page (PHP / ASP /ASP.NET/JSP ) and in that server page you can execute a query.
http://api.jquery.com/jQuery.ajax/
HTML
<input type='button' id='btnVote' value='Vote' />
Javascript
This code will be excuted when user clicks on the button with the id "btnVote". The below script is making use of the "ajax" function written in the jquery library.It will send a request to the page mentioned as the value of "url" property (ajaxserverpage.aspx). In this example, i am sending a querystring value 5 for the key called "answer".
$("#btnVote").click(function(){
$.ajax({
url: "ajaxserverpage.aspx?answer=5",
success: function(data){
alert(data)
}
});
});
and in your aspx page, you can read the querystring (in this example, answer=5) and
build a query and execute it againist a database. You can return data back by writing a Response.Write (in asp & asp.net )/ echo in PHP. Whatever you are returning will be coming back to the variable data. If your query execution was successful, you may return a message like "Vote captured" or whatever appropriate for your application. If there was an error caught in your try-catch block, Return a message for that.
Make sure you properly sanitize the input before building your query. I usually group my functionalities and put those into a single file. Ex : MY Ajax page which handles user related stuff will have methods for ValidateUser, RegisterUser etc...
EDIT : As per your comment,
jQuery support post also. Here is the format
$.post(url, function(data) {
alert("Do whatever you want if the call completed successfully")
);
which is equivalent to
$.ajax({
type: 'POST',
url: url,
success: function(data)
{
alert("Do whatever you want if the call completed successfully")
}
});
This should be a good reading : http://en.wikipedia.org/wiki/Same_origin_policy
It's just a few lines in your favorite language.
Javascript
$.post('script.php', { id: 12345 }, function(data) {
// Increment vote count, etc
});
PHP (simplified)
$id = intval($_POST['id']);
mysql_query("UPDATE votes SET num = num + 1 WHERE id = $id");
There are many different ways to accomplish this.

Alternate method for dojo.xhrGet() method

I am new to Dojo Framework.I created one button using dojo constructor and dojo.connect onclick event function i written url and load functions.This url navigating servlet and get the response back.
but i don't want response back i want to send request only.
how to do this..anyone help me.
thanks in advance.
are you looking to navigate to another page? if so, you can use window.location.href or other approaches to achieve that. See the foll url for other approaches:
JavaScript: Navigate to a new URL without replacing the current page in the history (not window.location)
if you do not want to navigate but just send some data to the server (and dont care about the response), you can just write an empty function for the callback
var deferred = dojo.xhrGet( {
url : "xxx",
load: function(data) {
//ignore
}
});
});
However, it is recommended to always check the response to ensure there were no errors on the server side.
You could also use dojo.xhrPost to submit your form

How to pass variables from an HTTPObject

I'm very, very new to Javascript, and to web programming in general. I think that I'm misunderstanding something fundamental, but I've been unable to figure out what.
I have the following code:
function checkUserAuth(){
var userAuthHttpObject = new XMLHttpRequest();
var url = baseURL + "/userAuth";
userAuthHttpObject.open("POST",url,true);
userAuthHttpObject.setRequestHeader("Content-type", "application/x-www-form-urlencoded");
userAuthHttpObject.onload=function(){
if (userAuthHttpObject.readyState == 4) {
var response = json.loads(userAuthHttpObject.responseText);
return response; //This is the part that doesn't work!
}
};
userAuthHttpObject.send(params);
}
I would love to call it from my page with something like:
var authResponse = checkUserAuth();
And then just do what I want with that data.
Returning a variable, however, just returns it to the userAuthObject, and not all the way back to the function that was originally called.
Is there a way to get the data out of the HttpObject, and into the page that called the function?
Working with AJAX requires wrapping your head around asynchronous behavior, which is different than other types of programming. Rather than returning values directly, you want to set up a callback function.
Create another JavaScript function which accepts the AJAX response as a parameter. This function, let's call it "takeAction(response)", should do whatever it needs to, perhaps print a failure message or set a value in a hidden field and submit a form, whatever.
then where you have "return response" put "takeAction(response)".
So now, takeAction will do whatever it was you would have done after you called "var authResponse = checkUserAuth();"
There are a couple of best practices you should start with before you continue to write the script you asked about
XMLHTTTPRequest() is not browser consistent. I would recommend you use a library such as mootools or the excellent jquery.ajax as a starting point. it easier to implement and works more consistently. http://api.jquery.com/jQuery.ajax/
content type is important. You will have have problems trying to parse json data if you used a form content type. use "application/json" if you want to use json.
true user authorization should be done on the server, never in the browser. I'm not sure how you are using this script, but I suggest you may want to reconsider.
Preliminaries out of the way, Here is one way I would get information from an ajax call into the page with jquery:
$.ajax({
//get an html chunk
url: 'ajax/test.html',
// do something with the html chunk
success: function(htmlData) {
//replace the content of <div id="auth">
$('#auth').html(htmlData);
//replace content of #auth with only the data in #message from
//the data we recieved in our ajax call
$('#auth').html( function() {
return $(htmlData).find('#message').text();
});
}
});

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