I'm trying to understand AJAX and JSON and I'm not sure I get it, there are methods and functions that are doing the same stuff...
You've got $.getJSON to retrieve JSON format data from server, and you have $.ajax + $.post + $.get + load() to send data data to the server?
Can I use all of those methods to send JSON data?
Really I'm confused! Help me figure this out.
All those are just shorthands for calling the $.ajax function.
load is for retrieving HTML and writing it to the DOM in one go. You want to load JSON.
get and getJSON use GET requests which are not well-suited for sending JSON data.
post does a POST request, but doesn't allow you to choose the contentType of the sent data
For sending JSON you should use the $.ajax function with its many options, see Send JSON data with jQuery.
An AJAX request is, at heart, an HTTP request. This is the same protocol which is used for all content on the Web (arguably, if it's not HTTP, it's not the Web) - loading a page, the images on the page, the CSS and JS includes, a submitted form, etc, etc.
As such, it inherits pretty much all of the flexibility of HTTP, meaning a generic function like jQuery.ajax ends up quite complex, with lots of options you don't normally need to worry about. This leads to the Shorthand Methods you mentioned, which bundle up common sets of options and functionality.
Among the things you might want to vary:
The "method" of the request: GET or POST (or less common ones like HEAD, PUT, DELETE...). A GET request is the simplest: request this URL, give me its contents; parameters to a GET request are shoved onto the "query string" of the URL. A POST request is how larger forms would be submitted on a normal page: the parameters are passed as a body of data separate from the URL and control headers; for an AJAX request this is often helpful to send a block of XML or JSON to a URL. This is a very broad overview, and there are many more distinctions in behaviour and meaning between the two.
The "content type" you want in the response (and, for a POST request, of the data you're sending). Not only does this tell both the server and the browser what data it is handling, ensuring it will pass it successfully, it can give jQuery (or whatever library) a hint of what to do next: if a call returns XML, you'll probably want to manipulate it as a DOM straight away; if it's JSON, you'll want to parse it as a JS object.
What you want to do once the data comes back. I've already mentioned parsing JSON or XML, but what if your response is actually a block of HTML that you want to inject straight into the parent page? Obviously you could do that yourself in the callback function, but again jQuery includes a shorthand form in the shape of .load().
All of the above are possible with jQuery.ajax, but you'd have to remember the parameters, even though you're falling into the same cases again and again, so chances are most of the time you'll be using whichever of the shorthands suits your needs at that moment.
Related
I understand that fetch() response lets you receive formData from a server. I searched for an example that implements this functionality but I didn't find a single one. All examples talk about uploading (posting) formData from a client to a server, but not vice versa. This doesn't explain the .formData() method of the response.
So, could you please direct me to any link that has an example that receives a form data from a PHP server using the .formData() method of a fetch() response.
Thank you
https://developer.mozilla.org/en-US/docs/Web/API/Body/formData demonstrates the basic idea:
response.formData()
.then(function(formdata) {
// do something with your formdata
});
But it's very unusual for a server to return data in formData format - I've never seen that happen. It's not actually a very convenient format when it's serialised. Normally a server will return plain text, HTML, JSON or XML (or binary file data, of course).
The "note" in yellow at the top of the documentation explains what it's mainly used for. It says:
This is mainly relevant to service workers. If a user submits a form
and a service worker intercepts the request, you could for example
call formData() on it to obtain a key-value map, modify some fields,
then send the form onwards to the server (or use it locally).
(It's important to realise that this can read from the body of an outgoing request as as well as an incoming response. And also that the comparable text(), json() blob() etc methods can all be used in both directions too - these methods are attached to the Body object. Both requests and responses can contain a Body. So actually these methods don't care if it's a request or a response, they simply try to read from the Body of whatever it happens to be.)
I'm want to (or think I need to) use AJAX to accomplish what I intend.
When clicking on a specific link in a list of links, I want to fill the HTML markup below with content of specific subpages. The data is naturally somewhere in the database and actually easily accessible with the CMS's API (I'm using Processwire).
I'm quite new to coding and especially AJAX and all documentation I find online only mention it in combination with a JSON file that would be loaded via AJAX.
However, I don't have a JSON file on the server, that means, according to my understanding, I would need to
store the data I need in a multidimensional php array,
use json_decode to create and then save that JSON-file on the server,
load that file via AJAX and process through more JS.
Let alone keep that JSON-file updated (or create a new one and delete the old one?) since new content will arrive periodically. It seems unnecessarily complicated to me, but what do I know.
There's got to be a better way…
Any help is appreciated.
AJAX is simply a way to make a request to the web server for information.
When you make an AJAX request you ask for a response from a file on a server. So, you can send an AJAX request to a PHP script for-instance.
The PHP script could return anything, JSON is common and very widely used response format, but XML might be another one you've encountered.
So, your request for information is made using AJAX, and the response you get back is JSON.
You don't need to store a JSON file on your server. You just need to make an AJAX request that returns current data in JSON format.
AJAX allows you to do asynchronous HTTP requests.
You can of course ask for a json file, but you can also (for example) call an API.
I suggest you start by reading the the getting started guide for AJAX in MDN:
https://developer.mozilla.org/en-US/docs/Web/Guide/AJAX/Getting_Started
I have been playing around with the jQuery library the last week or two.
Very handy! I am now playing with the AJAX requests to retrieve things such as the weather, current downloads and more, which have been going well so far!
I have now tried to connect up to my ISP to get my current data usage (peak, off peak etc).
When I use Chrome, I can manually type the variables into the URL and have the required JSON code show in the browser. The issue is, that it seems to return text/html instead of application/json.
When you go into developer tools, it shows text/html. This make it difficult for me to retrieve the data from my home server using AJAX and JSONP. See here for a failed query (but you can still see the text/html output, which is in a JSON format! Failed JSON Query on ISP
My question is, how could I get this data from the server URL, then make it into JSON that jQuery can read?
When I try the .load , $.get functions I run into Cross Origin Issues...
EDIT:Here is the PDF documentation for the API (Download at the bottom of the page)
Notice that I need to append certain values (user / pass / token). My ultimate aim is to have my JS read these values and store them.
The issue is, that it seems to return text/html instead of application/json.
That's a serverside issue. Go and file a bug report.
This make it difficult for me to retrieve the data
Not by itself. You should be able to override the settings how responses are parsed, e.g. in jQuery by using the datatype parameter.
using AJAX and JSONP
Notice that you cannot use JSONP, as it is not supported by that API (judging from the docs and a simple ?callback=test try). If you want support for that, file a bug report against the service provider.
When I try the .load, $.get functions I run into Cross Origin Issues...
Yes. They don't send CORS headers either. I suspect that this API is only used internally, and by devices that are not subject to a same-origin policy.
how could I get this data from the server URL, then make it into JSON that jQuery can read?
Use a proxy on your own server (that runs in the same domain as your app). It can also fix that content-type header.
For more details see also Ways to circumvent the same-origin policy, though most of the methods require cooperation of the service provider (to implement serverside features).
If i understand you correctly You ask for a certain value and it gives you a string. For most API's in the world they send a string that you have to parse into JSON or some language code. I would suggest looking at Parsing JSON Strings link. It explains how to take well formated strings and parse them into JSON readable objects.
var obj = jQuery.parseJSON( '{ "name": "John" }' );
alert( obj.name === "John" );
if you go on further and start using php take a look that Parsing JSON Strings with PHP
EDIT:
use .done() method to grab text from other pages after AJAX call.
$.ajax(...).done(function(html){
//do what you want with the html from the other page
var object = $.parseJSON(html)
}
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
If all I want to do is submit a form to a PHP processor with POST data and get the result, is there any reason to use the ajax method over the jQuery load method?
Using Ajax requires a bunch of code versus something very simple on one line in jQuery like this:
$("#myDIV").load("myProcessor.php", {field1: target.value});
Hmmm, maybe this only works well with one field? Sorry, just getting back into JS.
$(element).load(...) will automatically insert the server response into the selected element as html (jQuery documentation for .load()). This might result in your server exposing information about the request directly to the user, which is probably not what you're looking to do.
$.ajax() also allows very fine control over what happens during the request. You can accurately intercept exceptions and produce a callback when the request finishes succesfully. These are all reasons to use $.ajax() over $(element).load(...). However, if your only concern is sending the data in the POST header and working with the response, then using $.post with a callback function will probably be the simplest approach. http://api.jquery.com/jQuery.post/
The .load method is is roughly equivalent to $.get(url, data,
success) (src).
The .get method is a shorthand Ajax
function (src).
For a simple ajax call, .load is appropriate. Use .ajax if you want to deal with specials parameters.
PS: If you don't want a fat framework like jQuery, look here : http://microjs.com/#ajax
From jQuery website about load
This method is the simplest way to fetch data from the server. It is
roughly equivalent to $.get(url, data, success) except that it is a
method rather than global function and it has an implicit callback
function. When a successful response is detected (i.e. when textStatus
is "success" or "notmodified"), .load() sets the HTML contents of the
matched element to the returned data.
you can read difference between load ajax on StackOverflow.
But, load is not for submitting a form using post method. Both POST and GET are different methods and works differently, data submitted using GET method will be available in the $_GET array but not in the $_POST.