Message between multi-level elements (Polymer) - polymer

What's the best way to change data between different levels (in DOM) elements?
For example, I would like to save an REST service base URL in a variable on index.html (<template is="auto-binding"), so I could access this value from anywhere in the project, regardless of the hierarchy.
I guess <core-storage> would be an option, is it? What are the other options?
Thanks
Edit:
Just found my answer here: https://stackoverflow.com/a/24876397/2750721

As Trevor Dixon explained in an earlier answer you can use globals. Divshot does this for a lot of their apps (even before it was officially in the docs) but they use their own custom element for globals.
So far their is no silver bullet answer though. My experience so far is it depends on the situation as far as what is the best practice. Here are some generalizations I usually think about...
Global browser storage (<core-storage>, <local-forage>, pouchDB, IndexedDB, cookies, etc.)
Usage: this is great if you have data that you need to share with multiple elements, managing offline data, and for maintaining state/data across apps that utilize traditional browser page navigation
Considerations: can have limited space on client (localStorage has 5mb base as an example), usually synchronous API's (not for all though like Mozilla's localForage), limited to a single browser, can get complicated fast in maintaining state
Custom Events
Usage: great for to sharing small amounts of data and signaling across the application. Events are clean & bubble up throughout the DOM, ignoring shadow boundaries
Considerations: not good for large amounts of data, not optimal for Virtual DOM approaches, reliable & easy to use, limited to window & document lifecycle (refresh will not maintain data state)
Globals
Usage: Great for sharing small & large amounts of data across the app in JavaScript objects
Considerations: Maintenance & performance could issues if not tended to early on, Polymer has a built in mechanism for globals so it is easy to use, bound to the document & window lifecycle
Generally, no you'll use a combination of these strategies with a restful API that data is ultimately persisted to and synchronized with. this is not always the case but it is typical in modern JavaScript applications on the client.

I'd do something like what is suggested in the Polymer docs under "Supporting global variables". https://www.polymer-project.org/0.5/docs/polymer/polymer.html#global. Make an element that uses a function closure to share state between all instances of the element, then create an instance of that element any time you need access to the shared data.
Copied straight from the docs:
<polymer-element name="app-globals">
<script>
(function() {
// these variables are shared by all instances of app-globals
var firstName = 'John';
var lastName = 'Smith';
Polymer({
ready: function() {
// copy global values into instance properties
this.firstName = firstName;
this.lastName = lastName;
}
});
})();
</script>
</polymer-element>
Then use the element as you would any other. You can
access its properties using Polymer data binding or plain JavaScript:
<polymer-element name="my-component">
<template>
<app-globals id="globals"></app-globals>
<div id="firstname">{{$.globals.firstName}}</div>
<div id="lastname">{{$.globals.lastName}}</div>
</template>
<script>
Polymer({
ready: function() {
console.log('Last name: ' + this.$.globals.lastName);
}
});
</script>
</polymer-element>

You can use custom events to alert changes between multi-level element, e.g.
<component-1>
Polymer({
ready: function() {
this.addEventListener("data-change", function(e) {
this.data = e.detail.data;
});
},
</component-1>
<component-deep>
Polymer({
dataChanged: function() {
this.fire("data-change", {data: this.data});
}
});
</component-deep>

Related

How to load two forge viewers in single web page

I am trying to add two forge viewers in a single web page. I am using "react-forge-viewer" npm package to do that, but for some reason, only one viewer gets loaded and another one stays at "starting viewer..." state. It would be really great if anyone could help me resolve this problem.
I think this might be because of the dependency on class names or ID's.
Also, I want to synch their events in such a way that if I change camera view by dragging on on viewer same thing should reflect on another viewer as well.
You can easily fit multiple Viewers together, just be sure to initialize them separately with distinct container divs:
var viewer1 = new Autodesk.Viewing.Private.GuiViewer3D(document.getElementById('MyViewerDiv1'));
var viewer2 = new Autodesk.Viewing.Private.GuiViewer3D(document.getElementById('MyViewerDiv2'));
Autodesk.Viewing.Initializer(options1, function() {
viewer1.start();
viewer1.load(...);
});
Autodesk.Viewing.Initializer(options2, function() {
viewer2.start();
viewer2.load(...);
});
And you can sync the states of two viewers by subscribing to the CAMERA_CHANGE_EVENT, but beware pitfalls like endless loops - you can overcome this by implementing critical blocks to ensure only one viewer is exclusively requesting the other viewer to sync at any given time:
viewer1.addEventListener(Autodesk.Viewing.CAMERA_CHANGE_EVENT, function()
{
//critical block to prevent endless chained loop of events
viewer2.restoreState(viewer1.getState())
});
viewer2.addEventListener(Autodesk.Viewing.CAMERA_CHANGE_EVENT, function()
{
//critical block to prevent endless chained loop of events
viewer1.restoreState(viewer2.getState())
});
See a working sample here.
P.S:react-forge-viewer is a third party package not authored by Autodesk as is noted in its own README so you might need to contact its author if you have issues with it.

Polymer, observe global path, please

In Polymer 1.0 you can drop {{localPropFoo.bar}} and bar will be observed for changes if you use this.set('localPropFoo.bar', 'new value'); to update its value.
But what to do if you want to bind template to an external object which is out of your control? E.g., this {{window.globalFoo.bar}} won't be bound to bar changes because external code doesn't depend on Polymer and doesn't call this.set.
Demo on codepen
Using Object.observe manually requires extra code and doesn't work in FireFox (dirty checks of observe.js to the rescue).
I want to know what is the idiomatic way of data binding to external objects out of your control.
Polymer doesn't do observation out of the box, because:
Object.observe support is not ubiquitous and dirty checks are expensive.
Object.observe may be expensive on itself.
Supposed Solution
Catch changes yourself, call notifyPath, this.fire('global-foo-changed', {path: 'globalFoo.bar', value:...}, this.set and this.push.
They all dispatch corresponding non-bubbling (capturing) globalFoo-changed custom events (only when needed).
Why my global-foo-changed events affect only this element?
global-foo-changed events are capturing (non-bubbling).
Polymer elements listen for bubbling events by default.
For some reason these capturing listeners capture bubble events dispatched from the same element (not from its children). Demo on codepen.
You may patch polymer with this behavior (I don't understand how it works):
SharedGlobalsBehavior = {
properties: {
globalFoo: {
type: Object,
notify: true,
value: globalFoo
}
},
created: function() {
window.addEventListener('global-foo-changed', () => {
if (!event.detail || !event.detail.path)
return; // Property initialization.
this.notifyPath(event.detail.path, event.detail.value);
},/* if capturing */ true);
}
};
Why No Observation Out of the Box
...sometimes imperative code needs to change an object’s sub- properties directly. As we avoid more sophisticated observation mechanisms such as Object.observe or dirty-checking in order to achieve the best startup and runtime performance cross-platform for the most common use cases, changing an object’s sub-properties directly requires cooperation from the user.
Specifically, Polymer provides two methods that allow such changes to be notified to the system: notifyPath(path, value) and set(path, value), where path is a string identifying the path (relative to the host element).

Polymer: How many observers is my element maintaining?

Given an element instance, how do I see how many observers it's maintaining?
I'm trying to figure if either of these implementations is more expensive.
Polymer({
fooChanged: function() {
this.bar = foo.baz;
}
}
Polymer({
computed: {
'bar': 'foo.baz'
}
}
I suspect they're equivalent (except that one is watching foo, the other is watching the path) but I want to be sure.
Internally, Polymer uses uses Node.bind() to bind the property changes.
It will use PathObserver to watch 'foo.baz' and of course, it's slower to watch a computed object like that versus a single attribute.
https://www.polymer-project.org/docs/polymer/node_bind.html
You can check all the event listeners in the chrome dev tools. Select the ID in the console and on the right you have the "event listeners" tab.
See:
Using Chrome, how to find who's binded to an event?
But I doubt this will show you anything performance wise. I think it is better to use the CPU profile in the profiles tab in the chrome dev tools.

Binding to viewmodel via a context?

I am looking at using Polymer for a new project I am working on. I'm lucky enough to be able to target the latest version of Chrome only.
One of the reasons I am looking at Polymer is that I understand that is uses the new Object.observe for data-binding. (I think I am right in saying that, please correct me if I am not!)
One thing I would like to achieve is to be able to run my tests against my view models rather than using a gui testing tool.
...but as far as I can see, Polymer is setup for the web components to actually be the view models. Am I right in saying that? Now I've not looked into Polymer testing, but I expect that would mean having to have a DOM to test...
Now, I can add a "context" attribute to every web component and bind the JS view model to that and have all the bindings as {{context.prop}}, {{context.prop1}}, etc...
Is this going against any polymer principle - have I got completely the wrong idea?
Example element:
<polymer-element name="my-element" attributes="context">
<template>
<textarea value="{{context.prop}}"></textarea>
</template>
<script>Polymer({});</script>
</polymer-element>
Element use:
<my-element id="ele"></my-element>
<script>
var model = { prop: 'initial value' }
// wait for DOM to load - should really use some sort of "ready" event here...
setTimeout(
function() {
var ele = document.querySelector('#ele');
ele.context = model;
}, 3000);
Object.observe(model, function() { console.log('changed'); });
</script>

All-in-one location/hashchange history management library

First of all, I know there's libraries that provide polyfills for location.pushState/popState (History.js, Hash.js, jQuery hashchange), so please don't just link to those.
I need a more powerful library to achieve the following in a RIA:
User clicks a link
library is notified and loads context via Ajax (no complete reload!)
All <a> elements are leveraged with a click handler that
prevents page reloads in 2. (preventDefault) and
calls location.pushState instead / sets location.hash for older browsers
loaded content is inserted in page and replaces current content
Continue with 1.
Also, previously loaded content should be restored as the user navigates back.
As an example, klick through Google+ in Internet Explorer <10 and any other browser.
Is there anything that comes even close? I need support for IE8, FF10, Safari 5 and Chrome 18. Also, it should have a permissive license like MIT or Apache.
I believe Sammy.js ( http://sammyjs.org) (MIT-licenced) has the best focus on what you want to do, with its 2 main pillars being:
Routes
Events
I could quote from the docs but it's pretty straightforward:
setup clientside routes that relate to stuff to be done, e.g: update the view through ajax
link events to call routes, e.g: call the route above when I click an link. (You would have to make sure e.preventDefault is called in the defined event I believe, since this is an app decision really, so that can't be abstracted away by any library that you're going to use imho)
Some relevant docs
http://sammyjs.org/docs
http://sammyjs.org/docs/routes
http://sammyjs.org/docs/events
Example for a route: (from http://sammyjs.org/docs/tutorials/json_store_1)
this.get('#/', function(context) {
$.ajax({
url: 'data/items.json',
dataType: 'json',
success: function(items) {
$.each(items, function(i, item) {
context.log(item.title, '-', item.artist);
});
}
});
});
Or something like
this.get('#/', function(context) {
context.app.swap(''); ///the 'swap' here indicates a cleaning of the view
//before partials are loaded, effectively rerendering the entire screen. NOt doing the swap enables you to do infinite-scrolling / appending style, etc.
// ...
});
Of course other clientside MVC-frameworks could be an option too, which take away even more plumbing, but might be overkill in this situation.
a pretty good (and still fairly recent) comparison:
http://codebrief.com/2012/01/the-top-10-javascript-mvc-frameworks-reviewed/
( I use Spine.js myself ) .
Lastly, I thought it might be useful to include an answer I've written a while ago that goes into detail to the whole best-practice (as I see it) in client-side refreshes, etc. Perhaps you find it useful:
Accessibility and all these JavaScript frameworks
I currently use PathJS in one of my applications.
It has been the best decision that i have made.
For your particular usecase take a look at HTML5 Example.
The piece of code that that makes the example work (from the source):
<script type="text/javascript">
// This example makes use of the jQuery library.
// You can use any methods as actions in PathJS. You can define them as I do below,
// assign them to variables, or use anonymous functions. The choice is yours.
function notFound(){
$("#output .content").html("404 Not Found");
$("#output .content").addClass("error");
}
function setPageBackground(){
$("#output .content").removeClass("error");
}
// Here we define our routes. You'll notice that I only define three routes, even
// though there are four links. Each route has an action assigned to it (via the
// `to` method, as well as an `enter` method. The `enter` method is called before
// the route is performed, which allows you to do any setup you need (changes classes,
// performing AJAX calls, adding animations, etc.
Path.map("/users").to(function(){
$("#output .content").html("Users");
}).enter(setPageBackground);
Path.map("/about").to(function(){
$("#output .content").html("About");
}).enter(setPageBackground);
Path.map("/contact").to(function(){
$("#output .content").html("Contact");
}).enter(setPageBackground);
// The `Path.rescue()` method takes a function as an argument, and will be called when
// a route is activated that you have not yet defined an action for. On this example
// page, you'll notice there is no defined route for the "Unicorns!?" link. Since no
// route is defined, it calls this method instead.
Path.rescue(notFound);
$(document).ready(function(){
// This line is used to start the HTML5 PathJS listener. This will modify the
// `window.onpopstate` method accordingly, check that HTML5 is supported, and
// fall back to hashtags if you tell it to. Calling it with no arguments will
// cause it to do nothing if HTML5 is not supported
Path.history.listen();
// If you would like it to gracefully fallback to Hashtags in the event that HTML5
// isn't supported, just pass `true` into the method.
// Path.history.listen(true);
$("a").click(function(event){
event.preventDefault();
// To make use of the HTML5 History API, you need to tell your click events to
// add to the history stack by calling the `Path.history.pushState` method. This
// method is analogous to the regular `window.history.pushState` method, but
// wraps calls to it around the PathJS dispatched. Conveniently, you'll still have
// access to any state data you assign to it as if you had manually set it via
// the standard methods.
Path.history.pushState({}, "", $(this).attr("href"));
});
});
</script>
PathJS has some of the most wanted features of a routing library:
Lightweight
Supports the HTML5 History API, the 'onhashchange' method, and graceful degredation
Supports root routes, rescue methods, paramaterized routes, optional route components (dynamic routes), and Aspect Oriented Programming
Well Tested (tests available in the ./tests directory)
Compatible with all major browsers (Tested on Firefox 3.6, Firefox 4.0, Firefox 5.0, Chrome 9, Opera 11, IE7, IE8, IE9)
Independant of all third party libraries, but plays nice with all of them
I found the last too points most attractive.
You can find them here
I hope you find this useful.
i'd like to suggest a combination of
crossroads.js as a router
http://millermedeiros.github.com/crossroads.js/
and hasher for handling browser history and hash urls (w/ plenty of fallback solutions):
https://github.com/millermedeiros/hasher/
(based on http://millermedeiros.github.com/js-signals/)
This will still require a few lines of code (to load ajax content etc.), but give you loads and loads of other possibilities when handling a route.
Here's an example using jQuery (none of the above libraries require jQuery, i'm just lazy...)
http://fiddle.jshell.net/Fe5Kz/2/show/light
HTML
<ul id="menu">
<li>
foo
</li>
<li>
bar/baz
</li>
</ul>
<div id="content"></div>
JS
//register routes
crossroads.addRoute('foo', function() {
$('#content').html('this could be ajax loaded content or whatever');
});
crossroads.addRoute('bar/{baz}', function(baz) {
//maybe do something with the parameter ...
//$('#content').load('ajax_url?baz='+baz, function(){
// $('#content').html('bar route called with parameter ' + baz);
//});
$('#content').html('bar route called with parameter ' + baz);
});
//setup hash handling
function parseHash(newHash, oldHash) {
crossroads.parse(newHash);
}
hasher.initialized.add(parseHash);
hasher.changed.add(parseHash);
hasher.init();
//add click listener to menu items
$('#menu li a').on('click', function(e) {
e.preventDefault();
$('#menu a').removeClass('active');
$(this).addClass('active');
hasher.setHash($(this).attr('href'));
});​
Have you looked at the BigShelf sample SPA (Single Page Application) from Microsoft? It sounds like it covers how to achieve most of what you're asking.
It makes use of History.js, a custom wrapper object to easily control navigation called NavHistory and Knockout.js for click handling.
Here's an extremely abbreviated workflow of how this works: first you'll need to initialize a NavHistory object which wraps history.js and registers a callback which executes when there is a push state or hash change:
var nav = new NavHistory({
params: { page: 1, filter: "all", ... etc ... },
onNavigate: function (navEntry) {
// Respond to the incoming sort/page/filter parameters
// by updating booksDataSource and re-querying the server
}
});
Next, you'll define one or more Knockout.js view models with commands that can be bound to links buttons, etc:
var ViewModel = function (nav) {
this.search = function () {
nav.navigate({ page: 2, filter: '', ... }); // JSON object matching the NavHistory params
};
}
Finally, in your markup, you'll use Knockout.js to bind your commands to various elements:
<a data-bind="click: search">...</a>
The linked resources are much more detailed in explaining how all of this works. Unfortunately, it's not a single framework like you're seeking, but you'd be surprised how easy it is to get this working.
One more thing, following the BigShelf example, the site I'm building is fully cross-browser compatible, IE6+, Firefox, Safari (mobile and desktop) and Chrome (mobile and desktop).
The AjaxTCR Library seems to cover all bases and contains robust methods that I haven't seen before. It's released under a BSD License (Open Source Initiative).
For example, here are five AjaxTCR.history(); methods:
init(onStateChangeCallback, initState);
addToHistory(id, data, title, url, options);
getAll();
getPosition();
enableBackGuard(message, immediate);
The above addToHistory(); has enough parameters to allow for deep hash-linking in websites.
More eye-candy of .com.cookie(), .storage(), and .template() provides more than enough methods to handle any session data requirements.
The well documented AjaxTCR API webpage has a plethora of information with downloadable doc's to boot!
Status Update:
That website also has an Examples Webpage Section including downloadable .zip files with ready to use Front End(Client) and Back End(Server) project files.
Notably are the following ready-to-use examples:
One-way Cookie
HttpOnly Cookies
History Stealing
History Explorer
There are quite a bit other examples that rounds out the process to use many of their API methods, making any small learning curve faster to complete.
Several suggestions
ExtJs, see their History Example, and here are the docs.
YUI Browser History Manager.
jQuery BBQ seem to provide a more advanced feature-set over jQuery.hashcode.
ReallySimpleHistory may also be of help, though it's quite old and possibly outdated.
Note: ExtJs History has been extended to optimize duplicate (redundant) calls to add().
PJAX is the process you're describing.
The more advanced pjax techniques will even start to preload the content, when the user hovers over the link.
This is a good pjax library.
https://github.com/MoOx/pjax
You mark the containers which need will be updated on the subsequent requests:
new Pjax({ selectors: ["title", ".my-Header", ".my-Content", ".my-Sidebar"] })
So in the above, only the title, the .my-header, .my-content, and .my-sidebar will be replaced with the content from the ajax call.
Somethings to look out for
Pay attention to how your JS loads and detects when the page is ready. The javascript will not reload on new pages. Also pay attention to when any analytics calls get called, for the same reason.