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Webmaster Forum / HTML, CSS, Scripts / JavaScript / May 2006Download and cache page without displaying it?
Hello. I am looking for a way to download and cache a web page that the user has not yet requested, and write the web page to the browser cache without displaying it. My intention is to improve display performance when the user eventually requests the cached document. Is there a way to do this in Javascript? Thanks -Mark Mark said the following on 5/27/2006 2:32 PM: > Hello. > > I am looking for a way to download and cache a web page that the user has > not yet requested, and write the web page to the browser cache without > displaying it. And how can you ensure that the user is going to request it? Load it in a hidden IFrame, it will get cached and then if it is requested then it will half way do what you want it to do. > My intention is to improve display performance when the user > eventually requests the cached document. You are looking in the wrong direction.  SignatureRandy comp.lang.javascript FAQ - http://jibbering.com/faq & newsgroup weekly Javascript Best Practices - http://www.JavascriptToolbox.com/bestpractices/ > And how can you ensure that the user is going to request it? I can't be sure. But it is likely. The context is one in which the user is invited to scroll through a series of images which are displayed one-at-a-time (a server-side Perl CGI script retrieves the image information from a database and generates the web page.) I have improved performance quite a bit by preloading the image that will be displayed on the next page in the sequence. I'm just wondering whether I can take that a step further and preload the entire page. > Load it in a hidden IFrame, it will get cached and then if it is requested > then it will half way do what you want it to do. Thanks, I'll give that a look. > You are looking in the wrong direction. I am always happy to have someone point me in the right direction. You are welcome to blindfold me, spin me around a few times, and place a keyboard in my hand. . . -Mark >> Load it in a hidden IFrame, it will get cached and then if it is >> requested then it will half way do what you want it to do. > > Thanks, I'll give that a look. Hmm. . .recursion. Luckily there are only a few dozen images in the database. Mark said the following on 5/27/2006 3:01 PM: >> And how can you ensure that the user is going to request it? > > I can't be sure. But it is likely. The context is one in which the user is > invited to scroll through a series of images which are displayed > one-at-a-time (a server-side Perl CGI script retrieves the image information > from a database and generates the web page.) Is it a thumbnail scenario where the user browses through the thumbnails on a single page or does every image have it's own thumbnail on it's own page? > I have improved performance quite a bit by preloading the image that will be > displayed on the next page in the sequence. I'm just wondering whether I can > take that a step further and preload the entire page. Sure. That is the basis for AOL/Netscapes "Top Speed Technology" where it attempts to preload potential pages the user might load while the user isn't loading anything and thus it can be considered "download down time". >> Load it in a hidden IFrame, it will get cached and then if it is requested >> then it will half way do what you want it to do. [quoted text clipped - 6 lines] > welcome to blindfold me, spin me around a few times, and place a keyboard in > my hand. . . If the load time of a plain HTML document is large enough that you are attempting to speed up that load time, you may want to look at trimming down the page/HTML itself - if possible. But, trying to blanket preload any potential page that a user may go to is going to be a challenge on any page that has more than 2 or 3 links in it. SignatureRandy comp.lang.javascript FAQ - http://jibbering.com/faq & newsgroup weekly Javascript Best Practices - http://www.JavascriptToolbox.com/bestpractices/ > Is it a thumbnail scenario where the user browses through the thumbnails > on a single page or does every image have it's own thumbnail on it's own > page? One thumbnail per page. There are arrows to scroll forwards and backwards. > But, trying to blanket preload any potential page that a user may go to is > going to be a challenge on any page that has more than 2 or 3 links in it. Nope, I just want to preload the page that the user will be loading if he presses the forward scroll button. I tried it with an Iframe, and it did work. But of course the contents of the Iframe are interpreted and its scripts executed, which causes the next page in the scroll sequence to be downloaded. . .and then the next. . .and then the next. . . Ideally what I would like to do is create a new document object outside of any context where its contents would be interpreted. Just download it, and stick it in the browser cache. But my investigation so far has uncovered no apparent way to do this. I must use an Iframe, or create a document object in a new window context. In either case the downloaded page will be interpreted and its scripts executed, leading to recursion. -Mark Mark said the following on 5/29/2006 2:00 AM: >> Is it a thumbnail scenario where the user browses through the thumbnails >> on a single page or does every image have it's own thumbnail on it's own >> page? > > One thumbnail per page. There are arrows to scroll forwards and backwards. If the pages you are trying to preload are taking a while to load, something is wrong in the page you are trying to preload. If you are already loading the image, the only thing left to load is the html file and the time to load a html file should be negligent compared to the loading of the images. >> But, trying to blanket preload any potential page that a user may go to is >> going to be a challenge on any page that has more than 2 or 3 links in it. [quoted text clipped - 6 lines] > page in the scroll sequence to be downloaded. . .and then the next. . .and > then the next. . . Have your IFrame check to see if it is the top document or if it is in an IFrame. If it is not in an IFrame, load the next page. If it is in an IFrame, you do nothing. SignatureRandy comp.lang.javascript FAQ - http://jibbering.com/faq & newsgroup weekly Javascript Best Practices - http://www.JavascriptToolbox.com/bestpractices/ > If the pages you are trying to preload are taking a while to load, > something is wrong in the page you are trying to preload. If you are > already loading the image, the only thing left to load is the html file > and the time to load a html file should be negligent compared to the > loading of the images. You are correct. Preloading the image has improved performance substantially. I am just trying to eke out that last bit of performance to make the transition a bit "snappier." And of course the improvement would be even more noticeable to a user on dialup. > Have your IFrame check to see if it is the top document or if it is in an > IFrame. If it is not in an IFrame, load the next page. If it is in an > IFrame, you do nothing. Ah, good idea. Thanks, I will try that. -Mark Mark said the following on 5/29/2006 12:18 PM: >> If the pages you are trying to preload are taking a while to load, >> something is wrong in the page you are trying to preload. If you are [quoted text clipped - 6 lines] > make the transition a bit "snappier." And of course the improvement would be > even more noticeable to a user on dialup. Don't use independent pages then. Just preload the next image in the thumbnails and then change the image on the current page. The image itself is already preloaded, so it would just be a matter of changing it: document.images['imageName'].src = newImage And then preload the next image. SignatureRandy comp.lang.javascript FAQ - http://jibbering.com/faq & newsgroup weekly Javascript Best Practices - http://www.JavascriptToolbox.com/bestpractices/ > Don't use independent pages then. Just preload the next image in the > thumbnails and then change the image on the current page. The image itself [quoted text clipped - 3 lines] > > And then preload the next image. Sorry, I should have been more specific. The thumbnail appears with various text describing it (artwork title, price, availability, and so on.) So I do need to change the page. Mark said the following on 5/29/2006 3:34 PM: >> Don't use independent pages then. Just preload the next image in the >> thumbnails and then change the image on the current page. The image itself [quoted text clipped - 7 lines] > text describing it (artwork title, price, availability, and so on.) So I do > need to change the page. You can change the text on the page as well as the image. <URL: http://jibbering.com/faq/#FAQ4_15> IF you are preloading the image, you could get the text from the server as well and change the innerHTML of a div tag accordingly. SignatureRandy comp.lang.javascript FAQ - http://jibbering.com/faq & newsgroup weekly Javascript Best Practices - http://www.JavascriptToolbox.com/bestpractices/ > You can change the text on the page as well as the image. > > <URL: http://jibbering.com/faq/#FAQ4_15> > > IF you are preloading the image, you could get the text from the server as > well and change the innerHTML of a div tag accordingly. Hmm. . .I would still need to query the server to obtain the text to be displayed with the next image in the scroll order. How would I do that without loading a new HTML page? XMLHttpRequest, perhaps? Mark said the following on 5/29/2006 7:16 PM: >> You can change the text on the page as well as the image. >> [quoted text clipped - 6 lines] > displayed with the next image in the scroll order. How would I do that > without loading a new HTML page? XMLHttpRequest, perhaps? Perhaps XMLHTTPRequest but if it were me, I would just dynamically load a .js file that only needed to have two or three variables defined and a simple function call: var nextImage = "nextImagePath"; var nextImageText = "Text for next Image"; var anotherImage = true/false; someFunctionInThePageToUpdateIt(); Where anotherImage would be a boolean that the server could write out to let you know if there is indeed another image coming next or if you have reached the end of the line in which case the nextImageText could be: "You have reached the end of the Internet, there are no more images to see". (Seen that commercial?) Search the archives for "Dynamically load JS Files" along with my name. SignatureRandy comp.lang.javascript FAQ - http://jibbering.com/faq & newsgroup weekly Javascript Best Practices - http://www.JavascriptToolbox.com/bestpractices/ > Search the archives for "Dynamically load JS Files" along with my name. I can't find it. Can you post the URI? Mark said the following on 5/30/2006 4:53 PM: >> Search the archives for "Dynamically load JS Files" along with my name. > > I can't find it. Can you post the URI? function loadJSFile(fileURL){ var loadScript = document.createElement('script'); loadScript.type = "text/javascript"; loadScript.src = fileURL; document.getElementsByTagName('head')[0].appendChild(loadScript); } and then call it like this: loadJSFile('URL to .js File'); How much further you take that function depends on how far backwards compatible you want to go. It needs some feature detection for createElement, getElementsByTagName and appendChild. SignatureRandy comp.lang.javascript FAQ - http://jibbering.com/faq & newsgroup weekly Javascript Best Practices - http://www.JavascriptToolbox.com/bestpractices/ > function loadJSFile(fileURL){ > var loadScript = document.createElement('script'); [quoted text clipped - 6 lines] > > loadJSFile('URL to .js File'); Ok, but would this not require that I have a collection of javascript files defined on the server, one for each set of data that I plan to display to the client? If so, then I could still create the JS files programmatically on the server, but I would need to give them user-specific naming (including the user's IP and the system time in the JS filename for example.) I would also need a server-side cleanup routine to periodically dispose of orphaned JS files. If this is the case, then XMLHttpRequest() might be a better approach, no? Mark said the following on 5/31/2006 11:30 AM: >> function loadJSFile(fileURL){ >> var loadScript = document.createElement('script'); [quoted text clipped - 10 lines] > defined on the server, one for each set of data that I plan to display to > the client? Yes. But as I understand it, you have a collection of html files now that have that data and image and other HTML data in alreay. > If so, then I could still create the JS files programmatically on the server, > but I would need to give them user-specific naming (including the user's IP > and the system time in the JS filename for example.) No, you just need a static .js file for each image is all. Or, you could just have a DB with the data, and then a single server side script file that dynamically created the return data to the browser. > I would also need a server-side cleanup routine to periodically dispose of orphaned > JS files. No different than having to clean up orphaned HTML files now. > If this is the case, then XMLHttpRequest() might be a better approach, no? No. SignatureRandy comp.lang.javascript FAQ - http://jibbering.com/faq & newsgroup weekly Javascript Best Practices - http://www.JavascriptToolbox.com/bestpractices/ > I am looking for a way to download and cache a web page that the user has > not yet requested, and write the web page to the browser cache without > displaying it. My intention is to improve display performance when the > user eventually requests the cached document. > > Is there a way to do this in Javascript? There is no way at all. Because with regard to display performance, such attempts at preloading at first _decrease_ that performance in favor of the /generally/ less likely event that exactly the preloaded content is accessed later. Believe it or not, users /like/ incremental display. The obvious reason is that they can see, and possibly use, the top of the content /before/ the bottom is loaded. Don't get me wrong: This is not to say preloading is a Bad Thing. It is certainly useful (iff it works, you have no control over the cache features) if a dynamic effect needs to work regardless of known timing issues. But such /excessive/ preloading as you want it, is nonsense. PointedEars SignatureIndiana Jones: The Name of God. Jehovah. Professor Henry Jones: But in the Latin alphabet, "Jehovah" begins with an "I". Indiana Jones: J-... Thomas 'PointedEars' Lahn said the following on 5/29/2006 7:43 AM: >> I am looking for a way to download and cache a web page that the user has >> not yet requested, and write the web page to the browser cache without [quoted text clipped - 4 lines] > > There is no way at all. Yes there is. > Because with regard to display performance, such attempts at preloading > at first _decrease_ that performance in favor of the /generally/ less > likely event that exactly the preloaded content is accessed later. I suppose you use that same argument to tell people not to pre-load images? It is a flawed argument. Trying to preload the next page does not decrease the display performance for the current page if it is implemented correctly and uses the browsers "down time" for making HTTP Requests to the server. > Believe it or not, users /like/ incremental display. That has nothing to do with the question. It wasn't about trying to speed up the current page, it was about trying to speed up the transition from one page to the next. And no, users do not like to wait. Given the same exact content/pages, if a user is confronted with two scenarios: Scenario 1: Pages flow seemlessly, no wait. Scenario 2: User has to wait for the next page to load. The user will inevitably use the first page more often. > The obvious reason is that they can see, and possibly use, the top > of the content /before/ the bottom is loaded. That wasn't the issue. Please read it carefully again. > Don't get me wrong: This is not to say preloading is a Bad Thing. Huh? Even in this one post you are contradicting yourself. You say trying to preload decreases performance and argue against it, then you say it isn't a bad thing. Make up your mind please. > It is certainly useful (iff it works, you have no control over the cache > features) if a dynamic effect needs to work regardless of known timing > issues. But such /excessive/ preloading as you want it, is nonsense. "excessive preloading"? WTF are you smoking? Trying to preload one image and an HTML file is *not* "excessive preloading" by *any* stretch of the imagination. SignatureRandy comp.lang.javascript FAQ - http://jibbering.com/faq & newsgroup weekly Javascript Best Practices - http://www.JavascriptToolbox.com/bestpractices/ |
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