Not entirely sure if "persistent templates" is what I am after, this is the first time I am using a Javascript templating engine. I am curious if there is a way of keeping the template data intact for the purposes of re-rendering a document once it has been rendered...
An example -- I define a simple template snippet:
<div id="price">Price: {{current_price}}</div>
I render it:
var template = Hogan.compile($("#price").html())
$("#price").html(template.render(price_data))
Let's say I want to update the price information every X seconds (fire a request, grab JSON and push it back to #price), re-rendering the template fails as there is no {{current_price}} any more. I could just do something along the lines of $('#price').text('Price: ' + price_data) after a succesful request but I feel this somehow makes the idea behind using templates useless.
So the question is, what is a way to re-use templates on a document? Cache the template data into a variable and re-use it when rendering or is there a more clever way?
Thanks.
You shouldn't be using a thing as its own template, you'll run into all sorts of problems (especially once you start adding mustache tags to attributes, or conditionally showing html tags, or anything like that).
Make your template its own element on the page. And do yourself a favor and use a <script type="text/x-mustache"> tag for it.
Related
I have a page which has many buttons that perform an action with javascript. No problem here, just a html page and multiple .js file, one .js file for every action. Just to separate stuff a bit and make everything a bit more manageable. I will write a script to combine them all at deployment.
A lot of my javascript actions need html elements to function. For example to change a color the color.js needs a div with form elements so that user can change the color and press the button to save changes. The color.js binds functions to the onClick of the buttons and such. No problem here.
A problem comes up when there are many javascript actions using many html elements. All these html elements need to put into one html page. This makes managing things complicated. For example when i change the color field id i need to go to color.js and do the change. In addition i have to find the html element in my huge html page and also do the change.
Is it possible to put the html elements needed by my javascript actions into the .js file and somehow include it in my html page?
Of course i can escape all html elements and put it in a javascript variable and document.write it. But escaping is not a nice thing to do and changing html afterwards is quite painful.
I'm also not looking for a ajax function, cause with many different actions this will cause network problems.
Cheers for any thoughts on the subject!
You can use templates to generate dynamic HTML via JavaScript. Most of Templates Engines have the same implementation:
A template structure (DOM) or HTML string
A method to render the template
The data that fills the template (Array, Object)
Settings to configure the template engine
I have used some template engines, one of them is Hogan.js which has a friendly sugared-syntax, very easy to use, but lower performance. It implements the Mustache syntax.
Other template engine is in Underscore.js library, which provides no sugared-syntax but a native javascript syntax, giving more power, and best performance.
The last one that I have used is kendo-ui templates.Kendo UI templates have a heavy emphasis on performance over feature glut. It will trade convenient "syntax sugar" for improved performance.
If you want to try more engines, here you can get a lot of them:
Template-Engine-Chooser
By other hand, if you want just to load static HTML (e.g. an static view), you can use jQuery.load(url) to load data from the server and place the returned HTML into the matched element. .load() is a shorthand method of jQuery.ajax()
Recomendation: whichever option you choose, I recommend using cache, either to save the view or to save the compiled template, thus the performance is improved by avoiding request of the same resource.
I have some table that ng-repeat is building. the table contains a lot of data, and sometimes the build phase of the html is taking 10-20 seconds on weak computers.
So i've started to explore about building the html in the server, but the problem is that i'll loose the data-binding, and i'm needing it because i have inline edit functionality in the table.
The ultimate solution will be rendering the table in the server-side, with all the directives remaining including the ng-repeat, and on the client, makes the ng-repeat recognize that the html already has been rendered for the first time and not render it again, until the first change in the data.
In the Angular source code in the ngRepeatDirective, there is the "lastBlockMap" object that contain mapping betwee each element created by ng-repeat, to his scope, in that structure :
clone: [THE_ELEMET]
id: "005"
scope: ChildScope
and from reading this arcticle :
http://www.bennadel.com/blog/2443-Rendering-DOM-Elements-With-ngRepeat-In-AngularJS.htm
i've got to conclusion that if i'll create this object, and pass it somehow to the ng-repaat directive, the directive will know that the html is already been rendered and will not render it again.
The problem is how to pass such information to ng-repeat???
Any one encountered this situation??
P.S.
I'm familiar with all the "ngRepeat preformance" posts and arcticles and have tried a lot of other options before approaching this solution, so please try to help me with this one.
Second P.S.
Sorry for my english... :)
There is no solution for compile the html into loop in angular.
maybe you need to try clean the json data you try to render and make it as simple as you can, and if you include directive inside the table, try to render it after the table is done.
also, try to isolate the reason for the slowness, disable the inline edit and all the other featers inside the table.
Use prerender.io to render the html on the server side. It basically opens a phantomjs process and executes the JS on the server, and serves the output. Works pretty well.
I've had this same question when working with different templating systems in different languages in the past, so first,
The general question
I want to use a sub-template to include a certain UI component which might appear in different places on a number of different pages. This UI component requires certain CSS and JS files.
I want to Do The Right Thing with CSS and JS resources, which, as far as I know and in broad terms, is to a) combine as many as possible b) minify as much as possible and maybe c) put what I can at the end of my markup so the browser doesn't have to wait for them to load before displaying content.
So, if I've got various different UI components, as well as different headers and sidebars in different sections of the site, which all require their own special CSS and JS to function correctly, what's the best way for me to manage them through a templating system so that the final markup is as small and well-organised as possible?
Specifics of my situation
I'm working on a large legacy PHP site, on which, to give the original authors the benefit of the doubt, development may have begun before MVC became really mainstream, and before there were so many choices of frameworks around to use. So there is no consistent MVC framework, no routing, no templating (no ORM either, but that particular curse isn't as relevant here).
I'm going to have to keep things ticking over, squashing bugs and adding a few new features until a complete rewrite is usable, so I'm trying to breathe some sanity into things as I go along.
The easiest place to start seemed to be the views layer, for which I'm using TinyButStrong. An example of their sub-templates can be found here, but like I said, I think this is a very general question.
Things I've considered
With a more integrated framework I'd like to be able to do something like $view->add_js($foo), but transitioning to a full-blown framework is what other people are doing while I try keep the existing codebase seaworthy. There isn't even really enough consistent organisation of files to roll something like this by hand.
At the moment the best thing I can come up with is making a DOMDocument out of the view right before it's output and manipulating <link> and <script> tags at that point. I don't know if that's a bit crazy though. Given the generality of the problem I'd like to think that there's a known sensible way to go about it.
Many thanks for your input.
It's hard for the reader to know what can or cannot be done with your code base. A common way to handle this situation would be to pass parameters to the view template, and the template can then include conditional chunks or include sub-templates based on your parameters. This does not require a full-fledged framework, a stand-alone template engine should do. If your template engine supports inheritance there is a nice pattern for handling assets in your templates - check here for example http://symfony.com/doc/2.0/book/templating.html.
Manipulating the Dom for each request to handle this kind of thing seems bit unorthodox.
What you want in this situation is some form of template inheritance; that is, technology whereby a sub-template has access to areas in a 'parent' template, and can edit or replace content in those areas. Using this ability, CSS and JS required for a component included via a sub-template can be added in to the <head> element of the parent page.
In Twig, this is achieved using named blocks. First, you create your parent template (or layout, as it's called in Twig), e.g. index.html.twig. You include in it a named block like {% block myCss %}.
Next, to create a sub-template, you begin the template with the line {% extends ::index.html.twig %}. Then, the content of a block defined in the sub-template with the same name as a block in the parent template (in this case {% block myCSS %}) will get substituted into the parent template. To append rather than replace content in the parent template, use {{ parent() }} to include content already existing in the parent.
An example of this with code is available at the link given by #Basel Shishani. I've heard that Twig is modelled after Django, and template inheritance in Django looks very similar (with the exception of using {{ block.super }} instead of {{ parent() }}. There is a discussion of how to achieve the same ends in TinyButStrong.
As a wider point, the Assetic library looks like a very promising solution for managing CSS and JS assets, in order to avoid duplication (e.g. where the same JS file is required by multiple components/subtemplates), enable concatenation and minification of assets, and more. This presentation of its features gives more details.
I'd like to build my own, but I'm not sure about the best way to do it. A partial is a template that is only a part of another bigger template and which can be inserted into multiple other templates at will.
Templating itself is fairly basic, just string exctraction and concatenation, but clientside partials have me a little stumped.
Here are a few methods I thought about:
1,
I could write a javascript helper function that loads partials through ajax into some form of local storage I suppose, and all subsequent templates that require that particular partial would first look inside local storage. I think this method isn't very safe because local storage isn't always guaranteed. And if I can't save them into local storage, partials would result in too many ajax calls.
2, I could put them all into script tags inside my main html file. This would work reasonably well, especially with head.js (to enable parallel loading of script tags), but still - I think each script tag is a separate call to the server right? That doesn't exactly improve the situation.
3, I could put all templates into a single script tag (or html I guess) and manually filter through some kind of delimiter...like: "#template1(blabla template1 string) #template2(blablabla template2 string) and put those strings into globals.
This would result only into a single call to the server, all the rest is done on the client.
Suggestions? I have looked at existing templating engines, but I can't really determine how they do it. The code is pretty complicated
The approach I took to spec out template calls and on-demand loads for the spec/rewrite of jQuery templates is to pipeline it.
See section 9 of the (early) draft spec, and see the conformance suite tests at the bottom for an example of custom on-demand template loading (Testcase "Main calls and Loaded just in time!" is the relevant one).
The basic gist is that plugin loaders (written in JS) get to hook in between-parsing and compiling to inspect the parse tree. A plugin pass gets an object mapping template names to parse trees. If they see any partial template selectors (to use your parlance) they can try and load any unresolved templates using AJAX calls or file I/O on Node.js, and add the partials to the input object to cause the compiler to compile the just loaded partials along with the public templates.
Efficiency-wise, see the benchmarks. I'm in the process of migrating the code to github : https://github.com/mikesamuel/jquery-jquery-tmpl-proposal in case you want to collaborate.
I'm using Django and Apache to serve webpages. My JavaScript code currently includes a data object with values to be displayed in various HTML widgets based on the user's selection from a menu of choices. I want to derive these data from a Python dictionary. I think I know how to embed the JavaScript code in the HTML, but how do I embed the data object in that script (on the fly) so the script's functions can use it?
Put another way, I want to create a JavaScript object or array from a Python dictionary, then insert that object into the JavaScript code, and then insert that JavaScript code into the HTML.
I suppose this structure (e.g., data embedded in variables in the JavaScript code) is suboptimal, but as a newbie I don't know the alternatives. I've seen write-ups of Django serialization functions, but these don't help me until I can get the data into my JavaScript code in the first place.
I'm not (yet) using a JavaScript library like jQuery.
n.b. see 2018 update at the bottom
I recommend against putting much JavaScript in your Django templates - it tends to be hard to write and debug, particularly as your project expands. Instead, try writing all of your JavaScript in a separate script file which your template loads and simply including just a JSON data object in the template. This allows you to do things like run your entire JavaScript app through something like JSLint, minify it, etc. and you can test it with a static HTML file without any dependencies on your Django app. Using a library like simplejson also saves you the time spent writing tedious serialization code.
If you aren't assuming that you're building an AJAX app this might simply be done like this:
In the view:
from django.utils import simplejson
def view(request, …):
js_data = simplejson.dumps(my_dict)
…
render_template_to_response("my_template.html", {"my_data": js_data, …})
In the template:
<script type="text/javascript">
data_from_django = {{ my_data }};
widget.init(data_from_django);
</script>
Note that the type of data matters: if my_data is a simple number or a string from a controlled source which doesn't contain HTML, such as a formatted date, no special handling is required. If it's possible to have untrusted data provided by a user you will need to sanitize it using something like the escape or escapejs filters and ensure that your JavaScript handles the data safely to avoid cross-site scripting attacks.
As far as dates go, you might also want to think about how you pass dates around. I've almost always found it easiest to pass them as Unix timestamps:
In Django:
time_t = time.mktime(my_date.timetuple())
In JavaScript, assuming you've done something like time_t = {{ time_t }} with the results of the snippet above:
my_date = new Date();
my_date.setTime(time_t*1000);
Finally, pay attention to UTC - you'll want to have the Python and Django date functions exchange data in UTC to avoid embarrassing shifts from the user's local time.
EDIT : Note that the setTime in javascript is in millisecond whereas the output of time.mktime is seconds. That's why we need to multiply by 1000
2018 Update: I still like JSON for complex values but in the intervening decade the HTML5 data API has attained near universal browser support and it's very convenient for passing simple (non-list/dict) values around, especially if you might want to have CSS rules apply based on those values and you don't care about unsupported versions of Internet Explorer.
<div id="my-widget" data-view-mode="tabular">…</div>
let myWidget = document.getElementById("my-widget");
console.log(myWidget.dataset.viewMode); // Prints tabular
somethingElse.addEventListener('click', evt => {
myWidget.dataset.viewMode = "list";
});
This is a neat way to expose data to CSS if you want to set the initial view state in your Django template and have it automatically update when JavaScript updates the data- attribute. I use this for things like hiding a progress widget until the user selects something to process or to conditionally show/hide errors based on fetch outcomes or even something like displaying an active record count using CSS like #some-element::after { content: attr(data-active-transfers); }.
For anyone who might be having a problems with this, be sure you are rendering your json object under safe mode in the template. You can manually set this like this
<script type="text/javascript">
data_from_django = {{ my_data|safe }};
widget.init(data_from_django);
</script>
As of mid-2018 the simplest approach is to use Python's JSON module, simplejson is now deprecated. Beware, that as #wilblack mentions you need to prevent Django's autoescaping either using safe filter or autoescape tag with an off option. In both cases in the view you add the contents of the dictionary to the context
viewset.py
import json
def get_context_data(self, **kwargs):
context['my_dictionary'] = json.dumps(self.object.mydict)
and then in the template you add as #wilblack suggested:
template.html
<script>
my_data = {{ my_dictionary|safe }};
</script>
Security warning:
json.dumps does not escape forward slashes: an attack is {'</script><script>alert(123);</script>': ''}. Same issue as in other answers. Added another answer hopefully fixing it.
You can include <script> tags inside your .html templates, and then build your data structures however is convenient for you. The template language isn't only for HTML, it can also do Javascript object literals.
And Paul is right: it might be best to use a json module to create a JSON string, then insert that string into the template. That will handle the quoting issues best, and deal with deep structures with ease.
It is suboptimal. Have you considered passing your data as JSON using django's built in serializer for that?
See the related response to this question. One option is to use jsonpickle to serialize between Python objects and JSON/Javascript objects. It wraps simplejson and handles things that are typically not accepted by simplejson.
Putting Java Script embedded into Django template is rather always bad idea.
Rather, because there are some exceptions from this rule.
Everything depends on the your Java Script code site and functionality.
It is better to have seperately static files, like JS, but the problem is that every seperate file needs another connect/GET/request/response mechanism. Sometimes for small one, two liners code os JS to put this into template, bun then use django templatetags mechanism - you can use is in other templates ;)
About objects - the same. If your site has AJAX construction/web2.0 like favour - you can achieve very good effect putting some count/math operation onto client side. If objects are small - embedded into template, if large - response them in another connection to avoid hangind page for user.
Fixing the security hole in the answers by #willblack and #Daniel_Kislyuk.
If the data is untrusted, you cannot just do
viewset.py
def get_context_data(self, **kwargs):
context['my_dictionary'] = json.dumps(self.object.mydict)
template.html
<script>
my_data = {{ my_dictionary|safe }};
</script>
because the data could be something like
{"</script><script>alert(123);</script>":""}
and forward slashes aren't escaped by default. Clearly the escaping by json.dumps may not 100% match the escaping in Javascript, which is where the problems come from.
Fixed solution
As far as I can tell, the following fixes the problem:
<script>
my_data = JSON.parse("{{ my_dictionary|escapejs }}");
</script>
If there are still issues, please post in the comments.