Goal
I'm making a Chrome extension to perform some manipulations on my university's website since the layout to select a course is bad. For this I need to access elements to read their inner information and also copy their CSS to add certain information that I will obtain from a different site, in a way that fits the style of the page.
Problem
When I open the source code on the exact page I want to use, it doesn't display the correct HTML. Instead it shows the main page's code under the dev tool. The interesting part is that when I highlight a certain element the code shows up and I'm able to make changes within the tool. But if I try to call a specific element under the console using $(id) or $$(id) it would show either null or [].
This causes some problems to because I'm new to any sort of web-related development and I would like to see the complete source so that I can select the elements I want and manipulate the page the way I would like. Maybe there is something I'm overlooking? that's why I need your help.
Possible reasons
I tried many things and try to research and concluded that it might have to do with frames since the url is not changing. However I'm not able to find any resources to teach me about frames (I know nothing about it) if that's the actual problem.
If the problem is another I would appreciate any assistance in solving it or any work around that I am not aware of.
The reason is definitely the use of frames. There are multiple documents at play here, the top level document and each frame has it's own document. This is important because the JavaScript you are executing is 99.9999% the top level document and not a child frame's document. Due to this, it's not finding the DOM nodes because it doesn't search the frames' documents.
You may know that I totally fell in love with Dart and Polymer and once again, I have a question addressing those two technologies.
My application is a fairly compex polymer app written in Dart. There are some sort of "pages" whereas a page is shown once the user performed an action. The pages contain various types of content and the number of items can reach from zero to a few hundreds.
To enhance the user experience I've build a loader which you can register elements at and once all registered elements loaded, the page is shown. This works and feels pretty amazing but it's way to complicated to make sure to react on all the different states which can occur and overall I am not that happy with the loader thingy.
Thus I wanted to ask if there is anything in Dart or Polymer which helps me to show a loading indicator as long as not everything is fully loaded and once it is done, it hides the loader?
Use an HTML/CSS-only loading indicator and style it so that it becomes hidden when the unresolved attribute is removed from the body. See https://www.polymer-project.org/0.5/articles/styling-elements.html#preventing-fouc
I want to set up a number of tags within GTM (at the most 25) and noticed in the support section Google states too many can affect the size of the container as well as how much data the browser has to download. As a general rule of thumb is anyone able to tell me how many is too many?
This isn't really a question about GTM so much as content you put on your page in general. And in general, the more stuff you have on your page, the longer the page will take to load, and the longer things take to load, the longer the visitor has to wait for your site to be fully displayed and working.
So basically "too many" can loosely be equated with overall page load being "too long". You could have 100 tags that on average take a total of half a second to load (e.g. perhaps most of your tags just (potentially) execute 1 line of code like setting a variable), or you could have 1 tag that takes a minute+ to load (e.g. perhaps some code block for some 3rd party script hosted on a bad server that takes forever to respond and maybe also loads lots of other scripts and images and stuff).
So how long is "too long"? There's no "general rule of thumb" here, because it's highly subjective and based on what's in those tags, what your site is (the "theme"/purpose) and who your target audience is.
In fact, I'd say if we're going for "general rule of thumb" instead of "evaluate my specific circumstance", the only truly accurate answer here is to always be of the opinion that your site is taking too long to load, so that you always strive to make it load faster, or failing that, make it load in such a way that the visitor doesn't notice or have to wait before interacting with your site.
In any case, I guess the tl;dr of this is GTM is basically telling you it's not some magic box that gets delivered in the same amount of time regardless of what you put into it because that's not how the internet works.
I implemented infinite scroll like so:
new_page_value = 1;
$(window).scroll(function() {
if($(window).scrollTop() >= $(document).height() - $(window).height() - 200) {
new_page_value = parseInt(new_page_value) + 1;
get_page(new_page_value);
}
});
When the user almost reaches the bottom of the page (200px left) the function get_page() is called. This contains an ajax call that gets all the contents of the new page and appends it to the <body> of the document.
Now I just realized if my site gets big and instead of having 10 small pages I have a gazillion giant pages then the user's browser might crash if they are persistent enough to keep infinite scrolling for long time.
Would this be a possible solution to this problem:
I will keep appending the new pages to the document <body> until the 10th page, after that I will be replacing the <body> content entirely instead of appending. So using html() rather than append().
I just don't know if this will actually work to prevent crashes. Will .html() clear the "memory" of prior html that was brought in via ajax?
I really think this is a common issue for many sites with AJAX list content. So let's take an example at some of the most popular ( think of scale = experience ) websites and their solutions :
Google Images
If you check out images.google.com and you search for whatever, for e.g. "guiness", you will see a page full of results (actually the images are ajax loaded, not the html-code, so the page is with fixed height) and when you scroll at the bottom there is a button "Show more results". This might be solution one of your problem, but is it really necessary to place a button at the bottom after, for e.g. the 10-th page? I really think it is generally a good solution for page usability and memory leaks, but it is really not a necessary option as we can see in :
Facebook
Facebook Newsfeed is another story. There is a button "Show more posts", but I really don't know when exactly it is displayed rather than loading the next page of posts. It happened to me once to load 10-15 pages of posts, only by scrolling. And you know Facebook posts include videos, photos, AJAX comments and a lot of more Javascript fancy stuff, which take a lot of memory. I think they've managed to do this after a lot of research, how much of the users scroll to the bottom.
Youtube
Youtube has "Load more videos" at every page, so the solution is basically similar to Google, except that Google renders the whole html of the page and on scrolling just loads the images.
Twitter
Twitter supports infinite scrolling. Yep, they do it may be because tweet is 140 characters and they don't need to worry about memory so much. After all who is willing to read more than 1000 pages of tweets at one page load. So they don't have a button for "load more" and they don't need one.
So there are two solutions :
Use infinite scrolling ( you should consider how much content you load and how rich it is )
Use button : "Load More"
Most of all, you should not delete already loaded content of a list.
Nowadays everything is Javascript and Javascript has garbage collection, so it is very hard to unload the DOM ( if it has Javascript, not plain text ) and manage to remove the Garbage from Javascript. Which means that you won't free the whole allocated memory of the unloaded content from the browser.
Also think about of your requests, why would you need to load again something, that you have already loaded at first place. It costs another server request, meaning another database request and so on.
I have worked with this before and here are some of my thoughts:
a) If you are appending data to the memory page(s) at a time then it is not an issue, some browsers might not respond well but most of the lastest browsers will render without any problem so long as there is enough memory on the target machine, you could probably see how the ram usage increases as you append pages. Use chrome for this as each page is a separate process and it has an inbuilt task manager
b) regarding usage of html(), it indeed removes the markup but it does so at a heavy cost as it tries to take care of special conditions and has an overhead and accesses all the controls nested within the container that you are replacing (not sure about the last pat), but it has a cost. A simpler way to clear the DOM would be to use the innerHTML property and set it to empty, jquery does this but it is at a later point in the html() api. open up the api and look at the method.
using innerHTML
$("<selector>")[0].innerHTML=""
Also deletion of pages sounds weird to me as a user, what if I want to go back to the initial comments and please dont think about making it an infinite scroller too.. I have tried and given up after the number of bugs raised but we had a genuine use case for it and I had to stick a button up there, but this wasnt when the user scrolled away from the first page, this is when the user landed on a 3rd page but now needs to see the results above it.
Hope that answers your question and btw infinte scrolling is your friend use it, dont over engineer a case which will probably only be tested by your QA team. Its better to spend your effort somewhere else.
Yes it will, if i may suggest an idea after let's say 5 pages just delete the first page and append the new one instead of deleted all of the previous pages. good luck :)
I run into a common problem when trying to do AJAX development. Where possible, I like to try and just update data in an existing layout, and not the layout itself. For example, take the div below:
<div id="content-5">Here is some content</div>
I would get the updated value for content-5 from the server and just replace the contents of content-5 with the value. This makes a lot of sense for simple data replacements where the value is always going to be displayed in its pure form.
Sometimes the content is more complicated, and I have to actually get more than just raw data... maybe there is some logic to determine how a value is displayed and perhaps the style needs to be different depending on the data inside. In that case, I generally produce the HTML on the server side and inject the HTML into the element instead of just raw data.
Example: A status field from the controller comes back as "complete", but from the design doc, "complete" is supposed to show the user the text "Available" and it needs to be styled in a way different from other statuses.
Doing this in Javascript would require some in-depth view knowledge that the template layer probably already handles. The end result would be the same (code snippet below), but the difference is that there could possibly be some code duplication and a far more complicated Javascript layer.
<div id="content-5"><span class="success">Available</span></div>
Without fail, the requirement comes up that the system will need to handle "new" contents as well. The easiest solution to implement is to just get all of the content's at the same time so that I do not need to handle the extra complexity of injecting a new element instead of just replacing existing content.
So, I create a new template, wrap the contents in another element with an ID, and bulk replace all of the content divs at the same time any time there is a change.
<div id="allContent">
<div id="content-1">Some content A</div>
<div id="content-2">Some content B</div>
<div id="content-3">Some content C</div>
<div id="content-4">Some content D</div>
<div id="content-5">Some content E</div>
</div>
At some point, I have to wonder: Where is the line? At some point it feels like I'll eventually just be replacing the whole page with an AJAX request. Would this really be a problem?
I realize this may be pretty subjective, but what are some good strategies for determining to which level you should be replacing content with AJAX? Replacing just the data seems to be my preferred method when possible as it makes the AJAX controllers very simple. Replacing larger chunks of HTML from a template seems to be the easiest for handling more complicating layout and design issues and also feels like it could be more easily maintained. Are there other options I have not considered?
I expect there will be some discussion about manipulating the DOM programatically, but I personally really dislike this. The code ends up looking pretty horrible and really starts to integrate too much layout and design into the JS layer for my liking. Since I generally work with template libraries of some sort (whether raw PHP, PHP templates like Smarty or JSP in Java) it seems to make more sense to leave as much visual design there as possible.
EDIT
Based on the first few answers, it seems like this is being read as trying to keep the user on the same page but navigating around around the site or otherwise changing the page in a radical way with each update. The question is more about how to determine where the layout work for AJAX calls should happen and whether or not it is an acceptable practice to change large chunks of code with an AJAX request, knowing that replacement code may look nearly identical to what had been there before.
I think the most important requirement is the refresh requirement. If after several AJAX updates I hit refresh, the page I was just looking at should be the page that arrives. If the page reverts to a previous state for any reason then the URL is wrong. If for any reason your AJAX data is going to make the URL in the browser invalid then you should not be using AJAX to fetch that data.
There are exceptions, of course for data the is even newer than the last AJAX request. But that's obviously not what I'm talking about. A live chat screen could receive an update between the last AJAX request and the refresh. No big deal. I'm talking about the logical content and the URL describing it should always be in sync.
Complete personal opinion ex nihil, my rule of thumb is to change no more than 1 "panel" unit or 33% of the page whichever is less.
The basis for this is that the user should be able to clearly recognise the previous page state is related to the new state - how would you feel if you were suddenly teleported into the building to your right? Be gentle with your poor user.
There are also serious technical questions about the benefits of moving and inserting basically a page worth of data, which I think is a bit of an AJAX anti-pattern. What benefit does AJAX provide if you're going to do that?
Your specific question seems dependant on the supposition that the response coming back from your AJAX request isn't "just" data. This feels wrong to me from a separation of concerns point of view: I would expect a page to have all the layout information it requires already, the AJAX response itself to provide nothing more than dumb data/markup, and the JS event handler which created the request to sew the two together, MVC style. In that respect I think, yes, you're doing too much.
(by panel, I mean one logical design element - a menu, a ribbon, an item metadata panel, etc..)
edit: now that I think about it, I think SO's user profile page breaks my rule of thumb with those tab clicks
Depending on whether you want people to be able to to link to / bookmark etc the current page, you might want to navigate the user's browser.
This isn't a concern for some apps like GMail etc, and they won't ever refresh the page.
For myself, I tend to think it's a good practice to navigate the browser when navigating to a logically different place. eg. a person's profile vs. a list of their messages.
Sorry if this is vague, it's rather subjective :-)
A good guideline for something like this is to ask yourself, "Is this dynamic application 'content', or is it content-content?" Your use case sounds like application content that will change with each user. This is probably the best place for Ajax, but with everything, it's always nice not to just have one hammer. You don't want to do too much on one page. For instance, if one part breaks, the entire thing might, thereby frustrating the user.
Anywhere you're looking at actual page content or anything where the information is static, I strongly suggest avoiding the use of JavaScript, as it runs the risk of being invisible to search engines. Make sure anything linking to information like this is crawlable. The first step towards this is dynamic generation on the server side rather than browser side.
If you're using Smarty templates to produce a page, just fragment a template into various meaningful sections - news.tpl, email.tpl, weather.tpl - and have a master.tpl producing the structure of the page and calling child templates.
Then, if you're for example using an AJAX call triggered by a timeout to refresh the news, you can just call the server, cram the necessary data into news.tpl, and return the results into the news div you set up with master.tpl. This way your news layout is always following the pattern of news.tpl. (If you used JavaScript to manipulate formatting bits or set up event handling on document load, you'll need to attach that post-processing to fire after the AJAX call.)
You haven't really gotten specific about the types of things you're trying to replace here, and my initial reaction is that, if a single event is triggering multiple sections of the page to update at once, that's a sign that maybe you should be coallating those sections into a single display.
How much formatting gets done on the server end versus how much gets done on the client end with JavaScript? I'd say server-side formatting if possible, that way you have code that reflects discussions you've made about display layout and logic. Client-side formatting can be used for more interface-based issues - sorting rows in a table and alternating row colors with :odd and :even selectors, showing and hiding divs to create a "tabbed display" without hitting the server since the data won't change just from selecting a new tab, that sort of thing.
Finally, AJAX is one-way. If your web page is a view on a database, this isn't as much of a problem, but using AJAX manipulation to take the place of normal navigation is a terrible idea.
If you were habitually replacing the entire contents of a page using AJAX calls, I would agree that you have a problem. However, it appears to me that you are attempting to carefully think through the implications of your design and attempting, where possible, to avoid what annakata has called this "AJAX anti-pattern."
My rule is a bit simpler: as long as a substantial amount of context (e.g. menu on the left, header, various controls, page title, etc.) remains on a page, I am Ok with replacing almost anything with an AJAX call. That being said, I've never struggled with a page that has as much AJAX-generated code as you are.
I do have one question though: isn't it possible to encode state so that you can just replace some of the Divs in your example rather than all of them? If not, have you thought about doing so?