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I want to create a web application that displays data from a public api. I will use d3 (a javascript data-visualization library). I want to retrieve data from the api every ten minutes, and update my page (say it is traffic, or something). I have not built many web applications, how do I get the updates?

Should the js on the client side use a timer to request updates from the server side of my application (perhaps the application is written in Rails or node.js). The server then makes the api call and sends a response asynchronously? Is this called a socket? I have read that HTML5 provides sockets.

Or, perhaps an AJAX request?

Or, does the server side of my application create a timer, make the api call, and then "push" updates to the view. This seems wrong to me, there could be other views in this application, and the server shouldn't have to keep track of which view is active.

Is there a standard pattern for this type of web application? Any examples or tutorials greatly appreciated.

Brian Tompsett - 汤莱恩
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dt1000
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3 Answers3

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An AJAX request (XMLHttpRequest) is probably the way to go.

I have a very simple example of an XMLHttpRequest (with Java as the backend) here: https://stackoverflow.com/a/18028943/1468130

You could recreate a backend to receive HTTP GET requests in any other server-side language. Just echo back whatever data you retrieved, and xmlhttp.onload() will catch it.

Depending on how complex your data is, you may want to find a JSON library for your server-side language of choice, and serialize your data to JSON before echoing it back to your JS. Then you can use JavaScript's JSON.parse() method to convert your server data to an object that can easily be used by the client script.

If you are using jQuery, it handles AJAX very smoothly, and using $.ajax() would probably be easier than plain-old XMLHttpRequest.

http://api.jquery.com/jQuery.ajax/ (There are examples throughout this page, mostly-concentrated at the bottom.)

It really annoys me how complicated so many of the AJAX tutorials are. At least with jQuery, it's pretty easy.

Basically, you just need to ask a script for something (initiate the request, send url parameters), and wait for the script to give you something back (trigger your onload() or jqxhr.done() functions, supplying those functions with a data parameter).

For your other questions:

  • Use JavaScript's setTimeout() or setInterval() to initiate an AJAX request every 600000 milliseconds. In the request's onload callback, handle your data and update the page appropriately.
  • The response will be asynchronous.
  • This isn't a socket.
  • "Pushing" probably isn't the way to go in this case.
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Jackson
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If I understand correctly and this API is external, then your problem can be divided into two separate sub-problems:

1) Updating data at the server. Server should download data once per N minutes. So, it should not be connected to customers' AJAX calls. If two customers will come to the website at the same time, your server will make two API call, what is not correct.

Actually, you should create a CRON job at the server that will call API and store its' result at the server. In this case your server will always make one call at a time and have quite a fresh information cached.

2) Updating data at clients. If data at customers' browsers should be updated without refreshing the page, then you should use some sort of Ajax. It can make a request to your server once per X minutes to get a fresh data or use so-called long-polling.

Alex
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I think the most effective way to implement real time Web application is to use Web socket to push changes from the server rather than polling from the client side. This way users can see changes instantaneously once server notify that there is new data available. You can read more on the similar post.

I have tried using nodejs package called socket.io to make a real time virtual classroom. It works quite well for me.

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nnattawat
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