I've done some web-based projects, and most of the difficulties I've met with (questions, confusions) could be figured out with help. But I still have an important question, even after asking some experienced developers: When functionality can be implemented with both server-side code and client-side scripting (JavaScript), which one should be preferred?
A simple example:
To render a dynamic html page, I can format the page in server-side code (PHP, python) and use Ajax to fetch the formatted page and render it directly (more logic on server-side, less on client-side).
I can also use Ajax to fetch the data (not formatted, JSON) and use client-side scripting to format the page and render it with more processing (the server gets the data from a DB or other source, and returns it to the client with JSON or XML. More logic on client-side and less on server).
So how can I decide which one is better? Which one offers better performance? Why? Which one is more user-friendly?
With browsers' JS engines evolving, JS can be interpreted in less time, so should I prefer client-side scripting?
On the other hand, with hardware evolving, server performance is growing and the cost of sever-side logic will decrease, so should I prefer server-side scripting?
EDIT:
With the answers, I want to give a brief summary.
Pros of client-side logic:
Better user experience (faster).
Less network bandwidth (lower cost).
Increased scalability (reduced server load).
Pros of server-side logic:
Security issues.
Better availability and accessibility (mobile devices and old browsers).
Better SEO.
Easily expandable (can add more servers, but can't make the browser faster).
It seems that we need to balance these two approaches when facing a specific scenario. But how? What's the best practice?
I will use client-side logic except in the following conditions:
Security critical.
Special groups (JavaScript disabled, mobile devices, and others).
In many cases, I'm afraid the best answer is both.
As Ricebowl stated, never trust the client. However, I feel that it's almost always a problem if you do trust the client. If your application is worth writing, it's worth properly securing. If anyone can break it by writing their own client and passing data you don't expect, that's a bad thing. For that reason, you need to validate on the server.
Unfortunately if you validate everything on the server, that often leaves the user with a poor user experience. They may fill out a form only to find that a number of things they entered are incorrect. This may have worked for "Internet 1.0", but people's expectations are higher on today's Internet.
This potentially leaves you writing quite a bit of redundant code, and maintaining it in two or more places (some of the definitions such as maximum lengths also need to be maintained in the data tier). For reasonably large applications, I tend to solve this issue using code generation. Personally I use a UML modeling tool (Sparx System's Enterprise Architect) to model the "input rules" of the system, then make use of partial classes (I'm usually working in .NET) to code generate the validation logic. You can achieve a similar thing by coding your rules in a format such as XML and deriving a number of checks from that XML file (input length, input mask, etc.) on both the client and server tier.
Probably not what you wanted to hear, but if you want to do it right, you need to enforce rules on both tiers.
I tend to prefer server-side logic. My reasons are fairly simple:
I don't trust the client; this may or not be a true problem, but it's habitual
Server-side reduces the volume per transaction (though it does increase the number of transactions)
Server-side means that I can be fairly sure about what logic is taking place (I don't have to worry about the Javascript engine available to the client's browser)
There are probably more -and better- reasons, but these are the ones at the top of my mind right now. If I think of more I'll add them, or up-vote those that come up with them before I do.
Edited, valya comments that using client-side logic (using Ajax/JSON) allows for the (easier) creation of an API. This may well be true, but I can only half-agree (which is why I've not up-voted that answer yet).
My notion of server-side logic is to that which retrieves the data, and organises it; if I've got this right the logic is the 'controller' (C in MVC). And this is then passed to the 'view.' I tend to use the controller to get the data, and then the 'view' deals with presenting it to the user/client. So I don't see that client/server distinctions are necessarily relevant to the argument of creating an API, basically: horses for courses. :)
...also, as a hobbyist, I recognise that I may have a slightly twisted usage of MVC, so I'm willing to stand corrected on that point. But I still keep the presentation separate from the logic. And that separation is the plus point so far as APIs go.
I generally implement as much as reasonable client-side. The only exceptions that would make me go server-side would be to resolve the following:
Trust issues
Anyone is capable of debugging JavaScript and reading password's, etc. No-brainer here.
Performance issues
JavaScript engines are evolving fast so this is becoming less of an issue, but we're still in an IE-dominated world, so things will slow down when you deal with large sets of data.
Language issues
JavaScript is weakly-typed language and it makes a lot of assumptions of your code. This can cause you to employ spooky workarounds in order to get things working the way they should on certain browsers. I avoid this type of thing like the plague.
From your question, it sounds like you're simply trying to load values into a form. Barring any of the issues above, you have 3 options:
Pure client-side
The disadvantage is that your users' loading time would double (one load for the blank form, another load for the data). However, subsequent updates to the form would not require a refresh of the page. Users will like this if there will be a lot of data fetching from the server loading into the same form.
Pure server-side
The advantage is that your page would load with the data. However, subsequent updates to the data would require refreshes to all/significant portions of the page.
Server-client hybrid
You would have the best of both worlds, however you would need to create two data extraction points, causing your code to bloat slightly.
There are trade-offs with each option so you will have to weigh them and decide which one offers you the most benefit.
One consideration I have not heard mentioned was network bandwidth. To give a specific example, an app I was involved with was all done server-side and resulted in 200Mb web page being sent to the client (it was impossible to do less without major major re-design of a bunch of apps); resulting in 2-5 minute page load time.
When we re-implemented this by sending the JSON-encoded data from the server and have local JS generate the page, the main benefit was that the data sent shrunk to 20Mb, resulting in:
HTTP response size: 200Mb+ => 20Mb+ (with corresponding bandwidth savings!)
Time to load the page: 2-5mins => 20 secs (10-15 of which are taken up by DB query that was optimized to hell an further).
IE process size: 200MB+ => 80MB+
Mind you, the last 2 points were mainly due to the fact that server side had to use crappy tables-within-tables tree implementation, whereas going to client side allowed us to redesign the view layer to use much more lightweight page. But my main point was network bandwidth savings.
I'd like to give my two cents on this subject.
I'm generally in favor of the server-side approach, and here is why.
More SEO friendly. Google cannot execute Javascript, therefor all that content will be invisible to search engines
Performance is more controllable. User experience is always variable with SOA due to the fact that you're relying almost entirely on the users browser and machine to render things. Even though your server might be performing well, a user with a slow machine will think your site is the culprit.
Arguably, the server-side approach is more easily maintained and readable.
I've written several systems using both approaches, and in my experience, server-side is the way. However, that's not to say I don't use AJAX. All of the modern systems I've built incorporate both components.
Hope this helps.
I built a RESTful web application where all CRUD functionalities are available in the absence of JavaScript, in other words, all AJAX effects are strictly progressive enhancements.
I believe with enough dedication, most web applications can be designed this way, thus eroding many of the server logic vs client logic "differences", such as security, expandability, raised in your question because in both cases, the request is routed to the same controller, of which the business logic is all the same until the last mile, where JSON/XML, instead of the full page HTML, is returned for those XHR.
Only in few cases where the AJAXified application is so vastly more advanced than its static counterpart, GMail being the best example coming to my mind, then one needs to create two versions and separate them completely (Kudos to Google!).
I know this post is old, but I wanted to comment.
In my experience, the best approach is using a combination of client-side and server-side. Yes, Angular JS and similar frameworks are popular now and they've made it easier to develop web applications that are light weight, have improved performance, and work on most web servers. BUT, the major requirement in enterprise applications is displaying report data which can encompass 500+ records on one page. With pages that return large lists of data, Users often want functionality that will make this huge list easy to filter, search, and perform other interactive features. Because IE 11 and earlier IE browsers are are the "browser of choice"at most companies, you have to be aware that these browsers still have compatibility issues using modern JavaScript, HTML5, and CSS3. Often, the requirement is to make a site or application compatible on all browsers. This requires adding shivs or using prototypes which, with the code included to create a client-side application, adds to page load on the browser.
All of this will reduce performance and can cause the dreaded IE error "A script on this page is causing Internet Explorer to run slowly" forcing the User to choose if they want to continue running the script or not...creating bad User experiences.
Determine the complexity of the application and what the user wants now and could want in the future based on their preferences in their existing applications. If this is a simple site or app with little-to-medium data, use JavaScript Framework. But, if they want to incorporate accessibility; SEO; or need to display large amounts of data, use server-side code to render data and client-side code sparingly. In both cases, use a tool like Fiddler or Chrome Developer tools to check page load and response times and use best practices to optimize code.
Checkout MVC apps developed with ASP.NET Core.
At this stage the client side technology is leading the way, with the advent of many client side libraries like Backbone, Knockout, Spine and then with addition of client side templates like JSrender , mustache etc, client side development has become much easy.
so, If my requirement is to go for interactive app, I will surely go for client side.
In case you have more static html content then yes go for server side.
I did some experiments using both, I must say Server side is comparatively easier to implement then client side.
As far as performance is concerned. Read this you will understand server side performance scores.
http://engineering.twitter.com/2012/05/improving-performance-on-twittercom.html
I think the second variant is better. For example, If you implement something like 'skins' later, you will thank yourself for not formatting html on server :)
It also keeps a difference between view and controller. Ajax data is often produced by controller, so let it just return data, not html.
If you're going to create an API later, you'll need to make a very few changes in your code
Also, 'Naked' data is more cachable than HTML, i think. For example, if you add some style to links, you'll need to reformat all html.. or add one line to your js. And it isn't as big as html (in bytes).
But If many heavy scripts are needed to format data, It isn't to cool ask users' browsers to format it.
As long as you don't need to send a lot of data to the client to allow it to do the work, client side will give you a more scalable system, as you are distrubuting the load to the clients rather than hammering your server to do everything.
On the flip side, if you need to process a lot of data to produce a tiny amount of html to send to the client, or if optimisations can be made to use the server's work to support many clients at once (e.g. process the data once and send the resulting html to all the clients), then it may be more efficient use of resources to do the work on ther server.
If you do it in Ajax :
You'll have to consider accessibility issues (search about web accessibility in google) for disabled people, but also for old browsers, those who doesn't have JavaScript, bots (like google bot), etc.
You'll have to flirt with "progressive enhancement" wich is not simple to do if you never worked a lot with JavaScript. In short, you'll have to make your app work with old browsers and those that doesn't have JavaScript (some mobile for example) or if it's disable.
But if time and money is not an issue, I'd go with progressive enhancement.
But also consider the "Back button". I hate it when I'm browsing a 100% AJAX website that renders your back button useless.
Good luck!
2018 answer, with the existence of Node.js
Since Node.js allows you to deploy Javascript logic on the server, you can now re-use the validation on both server and client side.
Make sure you setup or restructure the data so that you can re-use the validation without changing any code.
There're many highload sites notify their users about new messages/topics runtime, without page reloading. How do they do that? Which approach do they use?
I assume there's two approaches:
"Asking" the server using JavaScript each time gap
Use websockets
By common opinion, the first one is too heavy for the server, since it produces too many requests.
About second one's behaviour in highload apps I know nothing, is it fine one?
So, which design approach to use to implement functions like "new msg available" properly without the need to reload the page?
The question rather about performance :)
WebSocket performance in the browser is not an issue, and on the server side there are performant implementations. As an example, Crossbar.io can easily handle 180k concurrent connections on a small server (tested in a VM on an older i5 notebook), and 10k/s messages - and both scale with the hardware (RAM and CPU respectively). Also: Something like Crossbar.io/Autobahn/WAMP gives you a protocol on top of WebSockets to handle the distribution of notifications to clients, making your life easier.
Full disclosure: I work for the company that works on Crossbar.io, and there are other WebSocket and PubSub solutions out there. Take a look at what best fits you use case and go with that.
I have a web page that references and initializes multiple instances of the same ASP.NET generic user control.
What I want to do, is to cache/store the entire contents (html) of those controls somewhere on the client using the jquery detach() method.
The solution of localStorage does not fit here as it has a limit to 5MB which is low for my needs.
For now, i am using a global variable and more specific a javascript array(key-value) to store the data.
What do you think of this solution? Will I notice any lags or performance issues on browser? Is there any limit for that global var?
Also, is there a better way to implement such a task?
For cross browser compatibility, you can try an AJAX call that pulls/increments in your massive data and cache the call (stored as JSON/JSONP). jQuery has a cache mechanism but the meat of the implementation is going to be on the headers of the page call. Specifically you're going to want to add Expires, Last-Modified, and Cache-Control on the pages you AJAX in.
Then you'll want to pull in the data asynchronously and do the appropriate UI manipulation (if needed).
You don't want to store massive data in a single variable since its going to take longer when it goes through the JS process.
localStorage is still an edge technology, is implemented differently across vendors, and isn't backwards compatible (although there are JavaScript libs that help mitigate backwards compatibility)
Cookies not big enough
On-Page JSON or JS Variable You lose abstraction and increase initial page weight (which is going to be unsatisfactory if you're on mobile)
Whatever implementation you do, I would run some simple benchmark performance tests so you have the metric to backup your code
This will cause browser lag and multiple issues. You can pretty much guarantee that a mobile browser isn't going to work in this scenario because no sensible mobile browser is going to let you download and store 5MB+ in the LocalStorage object. It is a really bad idea to put 5MB+ of HTML into the DOM of any browser and not expect any kind of performance issue.
If you're not concerned about mobile, then look at IndexedDB. It allows a greater amount of storage and it persists even after the session is closed. It is fairly well supported in recent Chrome and Firefox browsers, but requires IE10 or higher.
I've written a JavaScript-based Website that is able to enter, edit and solve Nonograms. As you may know, solving a nonogram is an NP-complete problem.
My first attempt was pure (single threaded) JavaScript. But on larger nonograms, Chrome showed its BSOD and killed the JS script after a few minutes. Next attempt was to use Web Workers. I split the solving algorithm so that each worker gets one row/column to solve and returns the result. This was an improvement and it was able to solve medium size nonograms. But still, sometimes the browser killed the JS VM showing the BSOD after some time plus the website was not really responsive as I would have expected since this is what Web Workers are made for, aren't they?
Just for "fun", I ported the solving algorithm to Python and used ajax requests calling a python script instead of Web Workers. Interestingly, it was even slower than JavaScript but after a some time of computation, the request returned a 500 Internal Server Error. I believe this is due to the maximum execution time of a CGI script which is 30s on PHP afaik.
The CGI idea was not the best because when multiple users want to solve a nonogram, the server runs on 100% CPU, so I probably stick with client side computation.
So question is, what is the best way to do this computation (which could take like 10min for larger nonograms)? I think the execution time is not an issue as long as the web site stays response and as long as the browser does not kill the execution tasks.
In the meantime, I'm also trying to optimize the recursive algorithm....
Thanks!
Maybe you could add some delay before you post messages to the WebWorkers. If the process is split up in to small enough functions, it may be possible to keep the page responsive, though it will take a lot longer to solve.
I'm currently writing a client-side javascript app which performs image manipulation. Some of the operations it performs currently are quite slow to run in the browser (taking in order of 2-3 seconds)
One solution I'm looking to implement is to have the client receive result information via a websocket from a server (websocket rather than AJAX because it needs to display realtime information etc.) and have the server do the heavy lifting of the image manipulation
Node.js is an obvious candidate being also written in Javascript - however my first thought is that there will be no performance advantage (my client side is running in Chrome/V8 and Node.js is also V8) - am I correct in thinking this? Or does the UI of Chrome necessitate performance losses on the client that won't be felt on the server side? (e.g. does Chrome do more UI work in the background to keep everything responsive that a node.js server wouldn't spend its time doing?)
Will node.js have any performance advantage at all, or am I better off looking into C or Java web socket servers to do the work?
The client is probably the better place to do image manipulation if you are doing it in javascript. The nice thing about the client is that you've got the processor (mostly) to yourself...if you have 20 people doing image manipulation at once, they will be doing it on 20 machines.
There are obviously some places where it makes more sense to do image manipulation on the server, and in those cases it may well be smart to consider using things other than javascript. V8 on the server isn't going to run much faster than on the client, and node isn't really made for cpu intensive tasks.
There are probably some interesting cases where you'll want to do interactive stuff on the client, and then do the final stuff on the server, and in that case there is a big advantage to node, since you can use the same code.
You should not determine where you will be doing calculations on server or client, based on the sole javascript execution speed.
Much more important are things like your estimated clients (desktop or mobile), server capacity and estimated average and peak load.