AJAX App JavaScript Loading Issue - javascript

I am creating a complete ajax application where there is one base page and any pages the user navigates to within the application are loaded via ajax into a content div on the page. On the base page I include the various scripts that are needed for every page within the application (jQuery, jQuery-UI, other custom javascript files). Then on the various pages with the application I include a script or two for each page that contains the logic needed for just that page. Each of those script files have something that executes on the page ready event. The problem is that every time the user navigates to page1, the page1.js file is loaded. So, if they visit that page 10 times, that script is then loaded ten times into their browser. Looking at the Chrome script developer tools after running around the site I see tons of duplicated scripts.
I read somewhere about checking to see if the script has already been loaded using a boolean value or storing the loaded scripts in an array. But, the problem with that is that if I see the script is already loaded and I don't load it, the page ready function doesn't get fired for the page's javascript file and everything fails.
Is there an issue having the javascript file loaded over and over when the user visit the same page multiple times?
I did notice looking at the network traffic that every time we visit the page, the script is requested with a random number parameter (/Scripts/Page1.js?_=298384892398) which causes the forced request for the script file every time. I set the cache: true settings on the jQuery ajaxSetup method and that removed the parameter from the request and thus the cached version of the javascript file was loaded instead of actually making a separate HTTP request for it. But, the problem is that I don't want all the ajax requests made to be cached as content changes all the time. Is there a way to force just javascript files to be cachced but allow all other ajax requests to be not cached.
Even when I forced caching on all requests, the javascript file still showed up multiple times in the developer tools. Maybe that isn't a big deal but it doesn't seem quite right.
Any advice on how to handle this situation?

About your first question:
Every time you load a JavaScript file, the entire content gets evaluated by the browser. It solely depends on the content if you can load and execute it multiple times in a row. I'd not consider it a best practice to do so. ;)
Still i'd recommend that you find a way to check if it was already loaded and fire the "page loaded" event manually within the already present code.
For the second question: I'd assume that the script is intended to show up multiple times when including it multiple times. To give an advice on how to not cache the loaded JS i'd need to know how you loaded the code, how you do AJAX and the general jQuery setup.

After doing some more research it looks like it is actually just a Chrome issue. When you load a script via AJAX you can include the following in your code to get it to show up in the the Chrome developer tools
//# sourceURL=some-script-name
The problem is that when you navigate away from the page, the developer tools keeps the script around, but it is actually not longer referenced by the page.

Related

How to apply JavaScript changes in Firebug?

I am playing around with a JavaScript code in Firebug and I would like changes to take effect in that page. Especially when there is code inside jQuery's $.ready() function.
Some kind of refreshing the page without losing of what has been edited. Is there any way to do that?
Page changes made via Firebug or via Javascript do not persist from one page load to another. Each time a page is loaded, the original HTML, CSS and JavaScript is parsed and loaded (from cache or from the server). Any prior changes will not be there.
The only way for a dynamic page change to be still present after a refresh is for you to save the changed state to a persistent location and then rebuilt the appropriate page content from that state each time the page is loaded.
But, if you make a change to the page and store some state in a cookie, in local storage or on your server, then you can have JavaScript that runs each time the page loads that gets that state from wherever you stored it and then applies the appropriate change to the page. If you're saving the state on the server (on behalf of this particular user), then you could even have the serve modify the page contents before it is served to the browser.
You can type JavaScript code in the Firebug command line and see changes take effect on the page. You can do the same in the Firefox, Chrome, Opera and Safari DevTools.
Changes to pages done via Firebug do not persist. After a page reload the original sources will be loaded again (from the server or the browser cache).
Currently Firebug doesn't allow you to edit the code of the loaded scripts directly.
Though you can execute JavaScript code within the context of the page by using the Command Line:
Or for longer scripts you can use the Command Editor:
But again, code you executed there will be gone as soon as the page is reloaded.
To make permanent changes to the JavaScript code of a page you need to have access to the server and make them there.

Downloading same JS file from 2 frames within parent page

I am working with a page that contains two frames. Each frame calls a page that then calls the same javascript file in a script tag. It appears that sometimes the browser will have cached the js file by the time the other frame makes its call, thus grabbing it from the cache. But, it appears that sometimes it downloads 2 copies, one for each frame. I'm trying to figure out if it would be worth calling the script once from the parent page and have each frame's page access it that way. So is it just a matter of how fast the browser happens to download the js file, if the other frame will grab it from the cache? What's the normal protocol for the major browsers on this?
Thanks for the help!
You can have the script look to see if it has any child iframes on the page, if it does, dynamically add a script block to the child document (with the same SRC). This way the main one will ALWAYS load first and the children will always use the cache.
I wouldn't worry too much about it. If by the time the second frame needs the file it's in the cache, then it'll use the cache, if not, it'll load it too. Each browser, and each version of each browser, handles caching of files differently, so just forget about it, code each frame as a page of its own with its own includes and let the browser worry about caching them.

Firefox reloads javascripts

I am a beginner web developer and here is my problem:
In short:
I keep getting similar message in Firebug for all the javascripts I include in the page:
GET http://localhost.:33085/Scripts/jquery.form.js?_=1284615828481 200 OK 1.01s
In details:
I am loading a webpage using AJAX . This page contains references to some java scripts. It also contains some embedded javascript code. Firefox keeps reloading the referenced java scripts each time I navigate to these pages which seems to take time. My questions are:
These scripts are already referenced in the page that has the where I load this page using AJAX. if I remove the references from this ajax loaded page, I start getting '$ is not defined'. Is there away to avoid that error other than referencing these scripts in the AJAX loaded page?
How can I stop firefox from reloading those pages and start using cached version?
Why is it so slow on firefox? I don't seem to see such perf issues on IE or Chrome?
Thanks
The best approach is to ensure that the initial page that you first access loads the required scripts and then subsequent ajax requests only load the content that you need (i.e. the references to the scripts is not in the html returned by the ajax request). There are server side frameworks to help you achieve this but without knowing your server technology I cant recommend a specific solution.
Firefox may be slow due to Firebug, with full debugging enabled in firebug it can slow you web pages down.

Getting browser to make an AJAX call ASAP, while page is still loading

I'm looking for tips on how to get the browser to kick off an AJAX call as soon as possible into processing a web page, ideally before the page is fully downloaded.
Here's my approximate motivation: I have a web page that takes, say, 5 seconds to load. It calls a web service that takes, say, 10 seconds to load. If loading the page and calling the web service happened sequentially, the user would have to wait 15 seconds to see all the information. However, if I can get the web service call started before the 5 second page load is complete, then at least some of the work can happened in parallel. Ideally I'd like as much of the work to happen in parallel as possible.
My initial theory was that I should place the AJAX-calling javascript as high up as possible in the web page HTML source (being mindful of putting it after the jquery.js include, because I'm making the call using jquery ajax). I'm also being mindful not to wrap the AJAX call in a jquery ready event handler. (I mention this because ready events are popular in a lot of jquery example code.)
However, the AJAX call still doesn't seem to get kicked off as early as I'm hoping (at least as judged by the Google Chrome "Timeline" feature), so I'm wondering what other considerations apply.
One thing that might potentially be detrimental is that the AJAX call is back to the same web server that's serving the original web page, so I might be in danger of hitting a browser limit on the # of HTTP connections back to that one machine? (The HTML page loads a number of images, css files, etc..)
You can use the jQuery onavailable plugin, which will execute as soon as an element is rendered on the page. You can have it execute once an element that is high up on the page renders.

How does caching work when a javascript file is loaded?

I have some tabs that are ajax powered. So everytime a tab is clicked all data is loaded including javascripts. So if they click on say Tab A then click on Tab B and finally Tab A. All Tab A scripts will be loaded twice.
Now I am wondering how does the caching work. On the second time they click on Tab A how much faster will these scripts download? Or will it be as slow as the first time?
Thanks
Assuming a fairly regular load, the script will load the first time, and be pulled from the cache from then on.
Unless you're doing something tricky.
Just like you can load a huge script on the first page request of a more traditional site, and include that script of subsequent pages, but after the first page load, the browser will (typically) just pull it from cache.
Use firebug and observe the behavior.
If you are loading the same URL, the browser will use the cached version. If you want to circumvent caching, add "?" followed by a random string to the url every time u call it.

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